Culex mosquitoes are important vectors of arboviruses such as West Nile virus, Eastern Equine Encephalitis virus and St. Louis Encephalitis virus. While these mosquitoes feed on a wide range of nectar sources consisting of many different carbohydrates, little is known about the utilization of these different carbohydrates for longevity and deposition of nutritional stores. In this study, the effect of feeding on different carbohydrates reported from natural food sources on longevity of three species of Culex was examined. Longevity was determined in the laboratory for male and female Culex nigripalpus Theobold, Culex quinquefasciatus Say and Culex salinarius Coquillet. Each were fed 5%(w/v) solutions of eight different sugars, a water control and one sugar mixture representing a common nectar source for mosquitoes. Carbohydrates tested included monosaccharides (d-glucose, d-fructose, sorbose). disaccharides (d-mannose, sucrose, trehalose) and trisaccharides (melezitose, raffinose). All sugars except sorbose supported greater longevity than the water controls. In general, the time to 50% and 100% mortality was shorter for males than for females for all sugars and species. Sugars tested included several of marginal nutritional value for other insects. These, however, supported longevity of mosquitoes well. Some significant differences in longevity between species and between sugars were detected and these data will be discussed in the context of disease transmission and vector competency.