Abstract: The acute toxicity of povidone iodine,trichloroisocyanuric acid,and lambda-cyhalothrin on Cyprinus carpio Songhe(118.8±5.63) cm in length,(72.75±15.11) g in body masswas investigated at a water temperature of (20±1)℃ using a static bioassay method.The results revealed that the median lethal concentration (LC₅₀) of povidone iodine was 870.551 mg/L at 24 h,790.650 mg/L at 48 h,694.959 mg/L at 72 h,and 654.692 mg/L at 96 h,with a safe concentration of 195.653 mg/L.For trichloroisocyanuric acid,the LC₅₀ was 23.076 mg/L at 24 h,19.608 mg/L at 48 h,15.674 mg/L at 72 h,and 13.871 mg/L at 96 h,with a safe concentration of 4.247 mg/L.The LC₅₀ of lambda-cyhalothrin was 4.620 mg/L at 24 h,2.216 mg/L at 48 h,1.205 mg/L at 72 h,and 0.847 mg/L at 96 h,with a safe concentration of 0.153 mg/L.The descending order of toxicity among the three substances to C.carpio Songhe was lambda-cyhalothrin>trichloroisocyanuric acid>povidone iodine.Based on toxicity evaluation criteria,povidone iodine and trichloroisocyanuric acid exhibited low toxicity for C.carpio Songhe and could be considered as the preferred choices in practical applications.However,lambda-cyhalothrin demonstrated high toxicity for C.carpio Songhe,requiring careful consideration and cautious use in practice.