Abstract: In this study, the polymorphism of S-indoxacarb was investigated to find the preponderant polymorph with the best insecticide activity. A novel S-indoxacarb polymorph form A was prepared by crystallization (isopropanol, ethanol). And amorphous form was also prepared by melting method. Polymorphs of S-indoxacarb characterized by powder XRD, TGA, DSC and FTIR spectra. 15% Suspension concentrate (SC) of S-indoxacarb form A and amorphous form were prepared, and their insecticide activities against Plutella xyllostella (L.), Chilo suppressalis (Walker)  were evaluated. The results showed the amorphous forms exhibited higher insecticide activity than that of polymorph A. This study confirms that S-indoxacarb has a polymorphic state and the amorphous form show better insecticide activity.