Protease inhibitors confer resistance in plants against insect pests by inhibiting larval gut proteases. Cultivars of Dolichos biflorus were screened for their inhibitory activity against midgut proteases of Pieris brassicae larvae. Seed extracts of developing and germinating seeds of HPK4 cultivar inhibited larval gut proteases of Spodoptera littoralis efficiently. Neonate larvae of P. brassicae fed on cabbage leaf discs coated with 0.025-2.50 mg protein (seed extract) resulted in 10-80% larval mortality and significantly reduced leaf area eaten and faecal matter as compared to control. The treated larvae had 40% less soluble proteins per mg faecal matter and there was similar decline in midgut proteases of treated larvae (@ 2.5 mg protein) compared to untreated ones after 5 days. The LC50 and LT50 value was calculated to be 1.05 mg/leaf disc and 4.8 days (2.5 mg protein), respectively for neonate larvae of P. brassicae. Significant reduction in egg hatching (75%) was observed in egg mass treated with 5.3 mg of crude inhibitor protein of mature seeds. This could be due to the inhibition of proteases involved in the hydrolysis of egg chorion proteins. The studies demonstrated the insecticidal activity of D. biflorus seed extracts.