Four insecticides, an organophosphate (malathion), a pyrethroid (delta methrin), an insect growth regulator (diflubenzuron) and a microbial (Bacillus thuringiensis), were tested as larvicides against Culex pipiens larvae which came from Qalyubia governorate. The present study revealed a large variation in the effectiveness of each insecticide against the C. pipiens larvae. Bacillus thuringiensis (LC90=0.0011 ppm) proved to be the most effective of the four. Deltamethrin followed with an LC90 of 0.004 ppm. Diflubenzuron with an LC90 of 0.076 ppm was third in terms of effectiveness. The least effective insecticide was malathion (LC90=0.67 ppm).