The cotton leafworm, Spodoptera littoralis (Boisd.) is very polyphagous insect against the most economic plants all over the world. The traditional synthetic chemical insecticides had dramatic effect on the living organisms including man. Anti-juvenile hormones; precocene II effect on the cotton leafworm, Spodoptera littoralis were assayed under laboratory conditions. (PrecoceneII (6,7-dimethoxy-2,2dimethylchromene) was the main constituent isolated from Ageratum houstonianum plant. The compound caused toxicity against the larvae with (LC10 was 5.59 mg/l), (LC25 was 24.69 mg/l) and (LC50 was 128.53 mg/l). There was some morphogenic effect obtained due to effect of precoceneII on larvae, pupae and adult stages. On the other hands the biochemical analysis of the cotton leafworm revealed that precocene II caused significant increase in chitinase, protease and total carbohydrates with (17.32, 50.17 and 36.85 %), respectively comparison to control.