The relative toxicity of emulsions of various pyrethroids was evaluated against the third instar larvae of Pieris brassicae in the laboratory. Except fenvalerate, the synthetic pyrethroids viz, deltamethrin, cyhalothrin, alphamethrin, bifenthrin, fenpropathrin and cyfluthrin were found to be highly toxic, their relative toxicity values being 23.2, 14.5, 10.5, 8.92, 7.73 and 6.12 times more compared to cypermethrin.