Abstract: This paper investigated the bioactivity of 10 pyrethroid insecticides to striped rice borer Chilo suppressalis (walker) in the lab. The results showed that the LD50 (μg/larva) of beta-cyfluthrin, lambda-cyhalothrin, esfenvalerate, deltamethrin, fenpropathrin, alpha-cypermethrin, beta-cypermethrin, cycloprothrin, etofenprox, and silafluofen to C. suppressalis are 0.0017, 0.0039, 0.0043, 0.0070, 0.0071, 0.0116, 0.0119, 0.714, 0.1779, 0.3858, respectively. Bioactivity of 5 formulations of lambda-cyhalothrin to C. suppressalis (walker) are different. The LC50 (mg/L) of EW, EC, ME, SC and WP formulations of lambda-cyhalothrin to C. suppressalis (walker) are 0.0945, 0.1089, 0.1174, 0.1232, 0.1591, respectively.