Culex pipiens was the main vector of Bancroftian filariasis that causes filariasis disease in Egypt. Effect of chlorpyrifos on field strains of C. pipiens in laboratory and their field breeding habitats were evaluated in village of Saft, Beni Suef Governorate, Egypt. Under laboratory conditions,  all tested concentrations (0.5-25 ppm) of chlorpyrifos caused complete mortality of the larval instars compared to the control treatment. While, the pupal mortality significantly increased with increasing concentrations of chlorpyrifos and the highest pupal morality of C. pipienswas obtained at 25 ppm. Under semi field trials, the highest morality in immature stages of C. pipienswas obtained at concentration of 25 ppmwhich were 100.0, 100.0 and 96.7% for second and fourth larval instars and pupal stage, respectively after 48 h. While in under field conditions, the complete reduction in density of immature stages of C. pipiens in treated cement tanks with chlorpyrifos was at 25 ppm after 24 h. The reduction in C. pipiens density was slightly lower in other breeding habitats (Agriculture canals and drains). In agricultural canals, the percentages of reduction in density of second and fourth instars and pupal stage were 95.3, 81.9 and 87.5%, respectively after 24 h, while in drains were 87.0, 70.9 and 50.0%, respectively. Our results were indicated that chlorpyrifos was effective on C. pipiens in most of their breeding habitats.