Abstract: This research was conducted to determine the effect of trypsin inhibitor on growth and development of Spodoptera litura. Trypsin Inhibitor from Momordica cochinchinensis (MMCTI) seed was extracted and purified using Ion Exchange Chromatography with CM-52 column. Trypsin Inhibitor Unit (TIU) was identified by using BApNA as substrate. The MMCTI showed 0.34 specific inhibitory units and mass numbers was 3165.03. In larval feeding studies, MMCTI were found to retard growth and development of S. litura. Larvae fed on diet containing MMCTI showed reduction in weight that was dose-dependent. Larval mortality ranged from 8 to 15% of the larval population. Reduction in pupal weight by 25% and pupal mortality by 27% were also observed with 12 TIU g-1 diet. Malformed adults (5-16%) were recorded as an effect of abnormal development. Fertility was affected as the egg-laying incidence reduced from 810 egg/female (control) to 298 egg/female (12 TIU g-1 diet). This result indicated that MMCTI is an efficient inhibitor of proteinases in the S. litura larvae. Being small peptide, it would be easy to express MMCTI in plants to confer protection against devastating pests such as S. litura.