This study was conducted to evaluate the larvicidal activity of Ocimum basilicum and Ocimum gratissimum aqueous leaf extracts against the larvae of Culex quinquefasciatus mosquito. The leaf extracts were hydrodistilled in the laboratory to obtain various concentration dosage of 500 ppm, 1500 ppm, 2500 ppm and 5000 ppm which were used in running the bioassay under laboratory conditions. The results obtained showed that the leaf extracts of the two plants exhibited larvicidal activity against the mosquito larvae. About 100 % larval mortality occurred at leaf concentrations of between 2500 ppm and 5000 ppm within 24 hr of the bioassay tests. O. gratissimum leaf extract which gave LC50 value of 920.0 ppm was more potent than O. basilicum leaf extract which produced LC50 of 1000 ppm. The results from this study suggest that aqueous leaf extract of O. basilicum and O. gratissimum are promising as larvicides against C. quinquefasciatus and could be useful as biodegradable larvicidal natural resource for the control of mosquitoes.