Oil of Mentha piperita L. (Peppermint oil), a widely used essential oil, was evaluated for larvicidal activity against different mosquito species: Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus by exposing IIIrd instar larvae of mosquitoes in enamel trays 6x4 inch(2) size filled to a depth of 3 inch with water. Of the three species tested Cx. quinquefasciatus was most susceptible followed by Ae. aegypti and An. stephensi. Application of oil at 3 ml/m(2) of water surface area resulted in 100% mortality within 24 h for Cx. quinquefasciatus, 90% for Ae. aegypti and 85% for An. stephensi For Ae. aegypti 100% mortality was achieved at 3 ml/m(2) in 48 h or 4 ml/m(2) in 24 h. For An. stephensi 100% mortality was observed at 4 ml/m(2) in 72 h. The emergence at 3 ml/m2 was also inhibited to a great extent and the few adults which emerged did not ovipost even after taking a blood meal. The oil showed strong repellent action against adult mosquitoes when applied on human skin. Percent protection obtained against An. annularis, An. culicifacies, and Cx. quinquefasciatus was 100%, 92.3% and 84.5%, respectively. The repellent action of Mentha oil was comparable to that of Mylol oil consisting of dibutyl and dimethyl phthalates.