| Missouri (State or other jurisdiction of incorporation or organization)     |   | 43-1311101 (I.R.S. Employer Identification No.) |
|---------------------------------------------------------------------------------------|--------|------------------------------------------------------|
|                                                                                  |   |                                                 |
| 3101 McKelvey Road, St. Louis, Missouri (Address of principal executive offices) |   | 63044 (Zip Code)                                |

|                      |   |                     |   |                    |   |                        |
|---------------------------|--------|--------------------------|--------|-------------------------|--------|-----------------------------|
| Large Accelerated Filer o |   | Accelerated Filer þ |   | Non-Accelerated Filer o |   | Smaller reporting company o |

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| Document                       | Part of Form 10-K |
|--------------------------------|-------------------|
|                           |              |
| Proxy Statement for the 2013   |              |
| Annual Meeting of Shareholders | III               |

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| Column A                        |   | Column B                       |   |   | Column C                     |   |   |   | Column D |                               |   |   |   |                | Column E |   |
|---------------------------------|--------|--------------------------------|--------|--------|------------------------------|--------|--------|--------|----------|------------------------------------|--------|--------|--------|---------------------|----------|--------|
|                            |   |                           |   |   | Additions                    |   |   |   |     |                               |   |   |   |                |     |   |
|                            |   | Balance at beginning of period |   |   | Charged tocosts and expenses |   |   |   |     | Charged to other accounts describe |   |   |   | Deductions describe |     |   |   |   |   | Balance at end of period |   |
| Reserve for doubtful accounts   |   | $                              | 110    |   |                         | $      | 190    |   | (1       | )                                  |   |   |   |                |     | $      | 77 |   | (9 | ) |   |   | $ | 223 |   |
| Reserve for inventory valuation |   | $                              | 659    |   |                         | $      | 247    |   | (3       | )                                  |   |   |   |                |     | $      | 553 |   | (4 | ) |   |   | $ | 353 |   |
| Deferred tax valuation          |   | $                              | 24,573 |   |                         |   |   |   |     |                               |   |   |   |                |     | $      | 2,436 |   | (5 | )(6)(10) |   |   | $ | 22,137 |   |

| Column A                        |   | Column B                       |   |   | Column C                     |   |   |   | Column D |                               |   |   |   | Column E            |      |
|---------------------------------|--------|--------------------------------|--------|--------|------------------------------|--------|--------|--------|----------|------------------------------------|--------|--------|--------|---------------------|-----------|
|                            |   |                           |   |   | Additions                    |   |   |   |     |                               |   |   |   |                |      |
|                            |   | Balance at beginning of period |   |   | Charged tocosts and expenses |   |   |   |     | Charged to other accounts describe |   |   |   | Deductions describe |      |   |   |   | Balance at end of period |   |
| Reserve for doubtful accounts   |   | $                              | 178    |   |                         | $      | 26     |   | (1       | )                                  |   | $      | -      |                |      |   | $ | 94 |   | (2) |   |   | $ | 110 |   |
| Reserve for inventory valuation |   | $                              | 879    |   |                         | $      | 454    |   | (3       | )                                  |   | $      | -      |                |      |   | $ | 674 |   | (4) |   |   | $ | 659 |   |
| Deferred tax valuation          |   | $                              | 22,053 |   |                         | $      | -      |   |     |                               |   | $      | 2,520  |                | (6)(7)(8) |   |   |   |   |   |   |   | $ | 24,573 |   |

| Column A                        |   | Column B                       |   |   | Column C                      |   |   |   | Column D |                               |   |   |   | Column E            |      |
|---------------------------------|--------|--------------------------------|--------|--------|-------------------------------|--------|--------|--------|----------|------------------------------------|--------|--------|--------|---------------------|-----------|
|                            |   |                           |   |   | Additions                     |   |   |   |     |                               |   |   |   |                |      |
|                            |   | Balance at beginning of period |   |   | Charged to costs and expenses |   |   |   |     | Charged to other accounts describe |   |   |   | Deductions describe |      |   |   |   | Balance at end of period |   |
| Reserve for doubtful accounts   |   | $                              | 2,356  |   |                          | $      | 497    |   | (1       | )                                  |   | $      | -      |                |      |   | $ | 2,675 |   | (2) |   |   | $ | 178 |   |
| Reserve for inventory valuation |   | $                              | 665    |   |                          | $      | 214    |   | (3       | )                                  |   | $      | -      |                |      |   | $ | - |   |   |   |   | $ | 879 |   |
| Deferred tax valuation          |   | $                              | 21,634 |   |                          | $      | -      |   |     |                               |   | $      | 419    |                | (6)(7)(8) |   | $ | - |   |   |   |   | $ | 22,053 |   |

|   | (1) | Reserving of doubtful receivable. |
|--------|-----|-----------------------------------|

|   | (2) | Recovery of receivables previously listed as doubtful. |
|--------|-----|--------------------------------------------------------|

|   | (3) | Increase reserve for slow-moving product. |
|--------|-----|-------------------------------------------|

|   | (4) | Write off of slow moving inventory. |
|--------|-----|-------------------------------------|

|   | (5) | Includes increase in effective tax rate in Hungary. |
|--------|-----|-----------------------------------------------------|

|   | (6) | Includes a reduction in required valuation allowance due to domestic net operating loss (“NOL”) utilization. |
|--------|-----|--------------------------------------------------------------------------------------------------------------------------|

|   | (7) | Reduction in required valuation due to non-qualified stock options deduction for which no cash benefit has been realized. |
|--------|-----|---------------------------------------------------------------------------------------------------------------------------|

|   | (8) | Increase NOL due to losses incurred in Mexico. |
|--------|-----|------------------------------------------------|

|   | (9) | Write-off of uncollectible receivable. |
|--------|-----|----------------------------------------|

|   | (10) | Includes a reduction in required valuation allowance due to foreign NOL utilization |
|--------|------|-------------------------------------------------------------------------------------|

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|   | By     | /s/ ZSOLT RUMY                                        |   |
|--------|--------|-------------------------------------------------------|--------|
|   |   | Zsolt Rumy, Chairman of the Board, President, and     |   |
|   |   | Chief Executive Officer (Principal Executive Officer) |   |
|   |   |                                                  |   |

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| Exhibit Index  |
|----------------|
|           |   |   |
| Exhibit Number |   | Description |
|           |   |   |
| 3.1            |   | Restated Articles of Incorporation of the Registrant dated October 7, 1992, filed as Exhibit 3.1 to Registrant’s Registration Statement on Form S-3 (Reg. No.333-143996) and incorporated herein by reference. |
|           |   |   |
| 3.2            |   | Certificate of Amendment of Restated Articles of Incorporation of the Registrant dated February 15, 1996, filed as Exhibit 3.2 to Registrant’s Registration Statement on Form S-3 (Reg. No.333-143996) and incorporated herein by reference. |
|           |   |   |
| 3.3            |   | Certificate of Amendment of Restated Articles of Incorporation of the Registrant dated February 7, 1997, filed as Exhibit 3.3 to Registrant’s Registration Statement on Form S-3 (Reg. No.333-143996) and incorporated herein by reference. |
|           |   |   |
| 3.4            |   | Restated By-Laws of the Registrant dated September 22, 1992, filed as Exhibit 3.4 to Registrant’s Registration Statement on Form S-3 (Reg. No.333-143996) and incorporated herein by reference. |
|           |   |   |
| 4.1            |   | Form of certificate for Common Stock, filed as Exhibit 4.1 to Registrant’s Registration Statement on Form S-1 (Reg. No. 33-51142) and incorporated herein by reference. |
|           |   |   |
| 4.2            |   | Amendment No. 1 to Loan and Warrant Agreement and Registration Rights Agreement among the Registrant and the Lender parties thereto, filed as Exhibit 4.2 to the Registrant’s Current Report on Form 8-K dated April 28, 2006 and incorporated herein by reference. |
|           |   |   |
| 4.3            |   | Form of Warrant, filed as Exhibit 4.4 to the Registrant’s Current Report on Form 8-K dated April 28, 2006 and incorporated herein by reference. |
|           |   |   |
| 4.4            |   | Amendment No. 2 to Loan and Warrant Agreement and Registration Rights Agreement, dated as of December 14, 2006, among the Registrant and the Lenders, filed as Exhibit 4.3 to the Registrant’s Current Report on Form 8-K dated December 14, 2006 and incorporated herein by reference. |
|           |   |   |
| 4.5            |   | Form of Warrant, filed as Exhibit 4.4 to the Registrant’s Current Report on Form 8-K dated December 14, 2006 and incorporated herein by reference. |
|           |   |   |
| 10.1           |   | Zoltek Companies, Inc. Amended and Restated Directors Stock Option Plan filed as Exhibit 10.1 to Registrant's Quarterly Report on Form 10-Q dated August 13, 1999 is incorporated herein by reference.* |
|           |   |   |
| 10.2           |   | Credit Agreement, dated April 27, 2012 by and among Zoltek Companies,Inc., Zoltek Corporation, Zoltek Properties, Inc , Engineering Technology Corporation, Zoltek Automotive, and Zoltek Composite Intermediates LLC, in favor of JPMorgan Chase Bank, N.A. filed as Exhibit 10.1 to Registrants Quarterly Report on Form 10-Q for the quarter ended June 30, 2012, is incorporated herein by reference. |
|           |   |   |
| 10.3           |   | Amended Credit Facility Agreement, dated June 1, 2012, between Raiffeisen Bank and Zoltek Zrt., the wholly owned subsidiary of Zoltek Companies,Inc., filed as Exhibit 10.2 to Registrants Quarterly Report on Form 10-Q for the quarter ended June 30, 2012, is incorporated herein by reference. |
|           |   |   |
| 10.4           |   | Zoltek Companies, Inc. 2003 Long-Term Equity Incentive Plan, filed as Appendix A to Registrant's definitive proxy statement for the 2002 Annual Meeting of Shareholders is incorporated herein by reference.* |
|           |   |   |
| 10.5           |   | Restated and Amended Uncommitted Credit Line Agreement, dated June 1, 2012, between Raiffeisen Bank and Zoltek Zrt., the wholly owned subsidiary of Zoltek Companies,Inc., filed as Exhibit 10.3 to Registrants Quarterly Report on Form 10-Q for the quarter ended June 30, 2012, is incorporated herein by reference. |
|           |   |   |
| 10.6           |   | Zoltek Companies, Inc. 2008 Director Incentive Plan, filed as Appendix A to the Registrant’s Proxy Statement on Schedule 14A filed on January 2, 2008 and incorporated herein by this reference.* |
|           |   |   |
| 10.7           |   | Zoltek Companies, Inc. 2008 Long Term Incentive Plan, filed as Appendix B to the Registrant’s Proxy Statement on Schedule 14A filed on January 2, 2008 and incorporated herein by this reference.* |
|           |   |   |
| 10.8           |   | Second Trade Agreement dated as of January 1, 2012, between Vestas Wind Systems A/S and Zoltek Companies, Inc., is filed herewith.*** |
|           |   |   |
| 10.9           |   | Joint and Several Guarantee Agreement, dated June 1, 2012, between Raiffeisen Bank and Zoltek Zrt., the wholly owned subsidiary of Zoltek Companies,Inc., filed as Exhibit 10.4 to Registrants Quarterly Report on Form 10-Q for the quarter ended June 30, 2012, is incorporated herein by reference. |
|           |   |   |
| 21             |   | Subsidiaries of the Registrant filed as Exhibit 21 to the Registrant’s Annual Report on Form 10-K for the fiscal year ended September 30, 2007 and incorporated herein by reference. |
|           |   |   |
| 23.1           |   | Consent of Ernst & Young LLP. ** |

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| 31.1   |   | Certification of Chief Executive Officer pursuant to Rule 13a-14(a) under the Securities Exchange Act of 1934, as amended is filed herewith.                                                                                                                                                                                                                                         |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |   |                                                                                                                                                                                                                                                                                                                                                                                 |
| 31.2   |   | Certification of Chief Financial Officer pursuant to Rule 13a-14(a) under the Securities Exchange Act of 1934, as amended is filed herewith.                                                                                                                                                                                                                                         |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                 |
| 32.1   |   | Certification of Chief Executive Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 is filed herewith.                                                                                                                                                                                                                 |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                 |
| 32.2   |   | Certification of Chief Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 is filed herewith.                                                                                                                                                                                                                 |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                 |
| *      |   | Management compensatory plan or arrangement                                                                                                                                                                                                                                                                                                                                          |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                 |
| **     |   | Previously Filed                                                                                                                                                                                                                                                                                                                                                                     |
|   |   |                                                                                                                                                                                                                                                                                                                                                                                 |
| ***    |   | Certain confidential portions of this exhibit have been redacted and filed separately with the Securities and Exchange Commission pursuant to a confidential treatment request in accordance with Rule 24b-2 of the Securities Exchange Act of 1934, as amended. The location of each omitted portion is indicated by a series of three asterisks in brackets (“[***]”). |