Company: MYI
Filing Date: 2025-10-03
Form Type: N-CSR
Source: 0001193125-25-230138
Chunk: 106

Company: BLACKROCK MUNIYIELD QUALITY FUND III, INC.
Filing Date: 2025-10-03
Form: N-CSR
Chunk 106
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(a)(1) Code of Ethics – See Item 2 (a)(2) Any policy required by the listing standards adopted pursuant to Rule 10D-1under the Exchange Act (17 CFR 240.10D-1)by the registered national securities exchange or registered national securities association upon which the registrant’s securities are listed – Not Applicable (a)(3) Section 302 Certifications are attached (a)(4) Any written solicitation to purchase securities under Rule 23c-1 –Not Applicable (a)(5) Change in Registrant’s independent public accountant – Not Applicable (b) Section 906 Certifications are attached

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized. BlackRock MuniYield Quality Fund III, Inc.

| By: |     | /s/ John M. Perlowski                                    |
|     |     | John M. Perlowski                                        |
|     |     | Chief Executive Officer (principal executive officer) of |
|     |     | BlackRock MuniYield Quality Fund III, Inc.               |

Date: September 23, 2025 Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

| By: |     | /s/ John M. Perlowski                                    |
|     |     | John M. Perlowski                                        |
|     |     | Chief Executive Officer (principal executive officer) of |
|     |     | BlackRock MuniYield Quality Fund III, Inc.               |

Date: September 23, 2025

| By: |     | /s/ Trent Walker                                         |
|     |     | Trent Walker                                             |
|     |     | Chief Financial Officer (principal financial officer) of |
|     |     | BlackRock MuniYield Quality Fund III, Inc.               |

Date: September 23, 2025