The seed oils (petroleum ether extract) of three plants, Azadirachta indica, Annona squamosa and Pongamia pinnata were tested against the cyclops, Mesocyclops leuckarti sensu lato. Out of the seed oils tested, oil of Pongamia pinnata produced excellent cyclopicidal action followed by Annona squamosa. There was, however, no activity with Azadirachta indica oil. Further examination of Chromatographic fractions of P. pinnata oil narrowed down activity to one of four fractions.