**Exhibit      12.1**

| 1.   | I                have                reviewed this annual report on Form 20-F of Syngenta                AG; |
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| 2.   | Based                on my                knowledge, this annual report does not contain any untrue statement                of a                material fact or omit to state a material fact necessary to make                the                statements made, in light of the circumstances under which such statements                were made, not misleading with respect to the period covered by this                annual report; |
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| 3.   | Based                on my                knowledge, the financial statements, and other financial information                included in this annual report, fairly present in all material respects                the financial condition, results of operations and cash flows of                the                company as of, and for, the periods presented in this annual                report; |
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| 4.   | The                company’s                other certifying officer and I are responsible for establishing and                maintaining disclosure controls and procedures (as defined in Exchange                Act                Rules 13a-15(e) and 15d-15(e) and internal control over financial                reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f))                for                the company and have: |
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|   | a) | Designed                such                disclosure controls and procedures, or caused such disclosure controls                and                procedures to be designed under our supervision, to ensure that material                information relating to the company, including its consolidated                subsidiaries, is made known to us by others within those entities,                particularly during the period in which this annual report is being                prepared; |
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|   | b) | Designed                such                internal control over financial reporting, or caused such internal                control                over financial reporting to be designed under our supervision, to                provide                reasonable assurance regarding the reliability of financial reporting                and                the preparation of financial statements for external purposes in                accordance with generally accepted accounting                principles; |
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|   | c) | Evaluated                the                effectiveness of the company’s disclosure controls and procedures and                presented in this annual report our conclusions about the effectiveness                of                the disclosure controls and procedures, as of the end of the period                covered by this annual report based on such evaluation;                and |
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|   | d) | Disclosed                in                this annual report any change in the company’s internal control over                financial reporting that occurred during the period covered by the                annual                report that has materially affected, or is reasonably likely to materially                affect, the company’s internal control over financial reporting;                and |
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| 5.   | The                company’s                other certifying officer and I have disclosed, based on our most                recent                evaluation of internal control over financial reporting, to the company’s                auditors and the audit committee of company’s board of directors (or                persons performing the equivalent                functions): |
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|   | a) | All                significant deficiencies and material weaknesses in the design or                operation of internal controls over financial reporting which are                reasonably likely to adversely affect the company’s ability to record,                process, summarize and report financial information;                and |
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|   | b) | Any                fraud,                whether or not material, that involves management or other employees                who                have a significant role in the company’s internal controls over financial                reporting. |
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|   | /s/                  Michael                  Mack |   |
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| Name:  | Michael                Mack                        |   |
| Title: | Chief                Executive Officer             |   |