Ethanolic, acetone and petroleum ether extracts of leaves from the Egyptian plant Cupressus sempervirens (Cupressaceae) were tested against 3^rd instar larvae of the mosquito Culex pipiens L. The obtained results indicated that petroleum ether extracts were more efficient than ethanolic and acetone extracts. The toxicity, based on Lc₅₀ values, are arranged in a descending order as follows: ethanolic (Lc₅₀ 263.6ppm) > acetone extract (Lc₅₀ 104.3ppm) > petroleum ether extracts (Lc₅₀  37.8 ppm). As shown by the present results, a remarkable reduction in both the pupation percent and adult emergence was obtained. Moreover, all plant extracts exerted a delayed toxic effect on the pupae and adults after treatment of larvae. Also, various degrees of morphogenic abnormalities were observed in the immature and adult stages. Thus, these results may provide an opportunity to develop alternatives to costly organic pesticides and environmentally hazardous chemicals with some available cheap plants which are uaually environmentally safe to different living organisms.