When Cyazofamid is formulated in accordance with a conventional formulation method, Cyazofamid is degraded in some cases. The problem to be solved by the present invention is to improve storage stability of the formulation by controlling degradation of Cyazofamid as an agricultural chemical active ingredient. The present invention provides a method for controlling degradation of an agricultural chemical active ingredient, Cyazofamid, which comprises using at least one stabilizer selected from the group consisting of epoxidized animal oil and/or vegetable oil, a nonionic surface active agent of polyoxyethylene, an anionic surface active agent of polyoxyethylene, polyhydric alcohol and a basic substance.
