The study aims to evaluate the toxicity and biological activity of Nigella sativa and Coumarin extracts on the cotton leaf worm, Spodoptera littoralis. Data indicated that mortality percentage of 2nd instar larvae gradually increased with increasing the concentration used of the two tested plant extracts. The mortality percent were ranged from 6 to -25, 11-49 and 18-65% after 3, 5 and 7 days of treatment with Nigella sativa, respectively, while the mortality percentages ranged from 11-38, 19-58 and 25-74% after 3, 5 and 7 days of treatment with Coumarin, respectively . After 48 hrs Coumarin gave the lowest consumed leaf area (cm2) treated 48 hrs than Nigella (as antifeedant effect). Taking into account larval survival after treatment by Nigella or Coumarin. It was observed that the larval feeding on food treated by either Nigella or Coumarin affected the larval duration, and had a significant latent effect on the pupal duration. Larval treatment by Coumarin treated larvae had shorter than Nigella. Results indicated that, Nigella sativa revealed reduction in invertase activity, but Coumarin had no effect on invertase . In contrast, Coumarin caused significant increase in the activity of trehalase, while Nigella sativa did not cause change on trehalase. Both plants extracts resulted in significant increase in amylase activity of larvae treated of S. littoralis larvae compared to untreated one. Also, Coumarin and Nigella caused significant reduction of total protein.