The present study was conducted to assess the larvicidal and insect growth regulatory activities of methanol extract of Sargassum cristaefolium against Spodoptera litura Fabricius. The efficacy of brown algal seaweed collected from the Manora coastal landscape against the polyphagous pest Spodoptera litura was tested in the laboratory. Among the various treatments subjected, the methanol extract of the seaweed with the lowest feeding rate at greater concentrations showed potential antifeedant activity. The larvicidal content was observed initially from 48 hours and steadily increased up to 72 hours, with a larval death rate of up to 75.98percent when compared to control. The larvae remained pupated with a minimal pupal deformity. At 15% concentration, the pupation to adult conversion ratio was 1:0.27, whereas the conversion ratio in control was 1:1.01. The insecticidal activity of the test brown algae was confirmed by these findings.