Heavy metals are environmental contaminants and their levels in the environment have increased in recent times as a consequence of anthropogenic activities. Mosquitoes serve as vectors of many vertebrate blood pathogens; Culex pipiens is a very common mosquito species in Egypt and is the predominant vector of Wuchereria bancrofti that causes filariasis or elephantiasis in humans. The present investigation was carried out to study the biological effects of exposure to selected heavy metal ions namely; cadmium (Cd), copper (Cu), lead (Pb) and mercury (Hg) on C. pipiens. Moreover, to study certain physiological effects such as effects on total carbohydrate, lipid and protein content of whole body, electrophoretic proteins and free amino acids of ovaries. In addition, the present investigation aimed to study the histopathological effects of heavy metals tested on the reproductive organs in males and females at the level of oogenesis and spermatogenesis.