The present study was designed to evaluate the larvicidal activity of two organic products namely L(+)-tartaric acid and thiourea against Culex quinquefasciatus larvae. The larvicidal activity of L(+)-tartaric acid and thiourea was tested against third instars larva of Cx. quinquefasciatus. Mortality was recorded at 24, 48 and 72 h of post-exposure. At different time intervals, LC50 and LC90 values were calculated. Exposure to three graded concentrations (1.00%, 1.20% and 1.40% w/v) of tartaric acid and thiourea result in significant larval mortality (p<0.05) that increased over time in both cases. No mortality was observed in non-target organisms such as Gambusia sp., Chironomus circumdatus, Poecilia reticulata and Diplonychus sp. following exposure to these compounds. Tartaric acid and thiourea may prove useful as potential mosquito control agents, but require field testing in natural larval habitat.