Abstract: In order to control Prodenia litura effectively, the toxicity of Bt strain K-1 to 3-instar larvae of Prodenia litura was determined.The fresh tobacco leaves were dipped in undiluted K-1 ferment filtrate and dilutions of 50, 100, 300, 500, 800, 1000 for 5 minutes, then air dried indoors, and 3-instar larvas of Prodenia litura were fed with such treated tobacco leaves.The results indicated that the effect of treatment with undiluted K-1 ferment filtrate was the best and all of the larvae died in 72h after treating.The duration of infected time affected the toxicity prominently, the toxicity of Bt to Prodenia litura was enhanced obviously with the prolongation of infected time.