The insect antifeedant and toxic activity of two marine plants, Hibiscus tiliaceus and Sonneratia caseolaris on the herbivorous insects, Spodoptera litura F. were tested in the laboratory. The crude extracts were further purified in a column and their purified fractions were assessed for their antifeedant and insecticidal activity. The leaves extracted separately with acetone yielded crude extract which showed significant antifeedant activity to the 2nd as well as 3rd instar larvae of S. litura. The topical application of the plant crude extracts resulted in causing toxicity to the lepidopteran pest which was not more than 50 per cent with both the plant treatments. The extracts had considerable effect on the S. litura metamorphosis in the form of a delayed pupal formation and morphogenetic abnormalities in pupae due to the larval treatment, which affected the percentage adult eclosion. The crude leaf extract possesses moderate insecticidal activity to three of the major stored product pests, the flour beetle, Tribolium castaneum H., the rice weevil, Sitophilus oryzae L. and the lesser grain borer Rhyzopertha dominica (F.). All eluted fractions from H. tiliaceus and S. caseolaris have shown excellent antifeedant activity on S. litura than crude extracts. Particularly hexane eluted fraction of the crude extracts of both the marine plants showed potent growth inhibitory activity. We infer that the marine dwelling plants H. tiliaceus and S. caseolaris extracts has good feeding inhibitor activity to S. litura and a moderate toxicity to three of the major stored product pests.