Abstract Cyfluthrin and tetramethrin are extensively used synthetic pyrethroid pesticides. The present study was designed to compare the responses of two synthetic pyrethroids in carp (Cyprinus carpio). The experiments were repeated 3 times and 96-h LC50 values were determined for the carps. Lethal doses of the insecticides were determined using LC50 software programme of US EPA based on Finneys Probit Analysis statistical method. Behavioral changes of carps were also observed. The 96-h LC50 values of cyfluthrin and tetramethrin were estimated as 21.5 μg/L and 14.84 μg/L, respectively.