Population density and seasonal fluctuations of Culex pipiens (L.) immature stages were detected through one year from April, 1997 to March, 1998. Also, certain physical and chemical water properties affecting its habitats were concerned. Larval densities reached their maximum during July, 1997 (2943 and 2371 larvae) and October, 1997 (2644, 2226 larvae) in agricultural drains and small pools with stagnant water respectively. While, minimum density was recorded in sewage water (2039 larvae) during July. Significant differences in spring and winter, highly significant in autumn and insignificant differences in summer were found between larval population in all types of water. High pupal densities were established in small pools with stagnant water (2731 pupae) and agricultural drains (2614 pupae) with peaks observed through July and October low densities were recorded in both sewage water and mixed drains (2223 and 2204 pupae respectively. Significant differences in spring, highly significant in winter and insignificant differences in summer and autumn were recorded among pupal populations in all types of water. Highly significant correlation was found between temperature and both larval and pupal population in all types of breeding sites. Finally, two peaks of population density of the immature stages (larvae and pupae) were recorded through July and October, 1997 and the population density was markedly decreased throughout the period extended from November, 1997 to February, 1998. Highly significant correlation was found between larval and pupal populations during the year of study. Results showed that larvae of C. pipiens preffered water with pH ranging between 8.15 – 8.70 and the electric conductivity (E.C.) was ranged between 0.815 – 2.0 ds/m. C. pipiens larvae tolerate high concentrations of organic materials as indicated from nitrogen compounds such as ammonia (8.1 – 23.85 mg/L) and nitrate (31 – 35.65 mg/L) and biological oxygen demand (B.O.D.) (5 – 14 mg/L) in breeding sites. Also, they tolerate high salinity as indicated from total soluble salts ranging from 521.6 – 1216 mg/L. The chloride concentrations ranged between 31.95 – 159.72 mg/L. in the afforementioned aquatic larval habitats.