The influence of population density; prey density, stage, and type on the life history of the mosquito predator Sphaerodema urinator Duf was studied. Nymphal duration and mortality were increased and weight of adult males and females were decreased with the increase in rearing density. Adults reared in crowded conditions had shorter oviposition period, longer postoviposition period, lower fecundity and fertility, small weight and shorter longevity than those reared in low density. Nymphs and adults of S. urinator were able to feed equally on either larvae or pupae of Culex pipiens mosquito. Nymphs reared in high prey density had shorter duration and heavier weights than those reared on low prey density. S. urinator females fed on Culex pipiens larvae had significantly better fecundity, fertility, longevity and heavier weights than those fed on the alternative preys provided (Eristalis sp. and Orthetrum sp). Key Words: Sphaerodema urinator, predator density, prey density, prey stage and type, life history. mona.mansour@fsc.bu.edu.eg