Objective:To determine the mosquito larvicidal activities of hexane,chloroform,ethyl acetate, acetone and methanol leaf extract of Orthosiphon thymiflorus(O.thymiflorus) against Anopheles stephensi(An.stephensi),Culex quinquefasciatus(Cx.quinquefasciatus) and Aedes aegypti (Ae.aegypti).Methods:The larvicidal activity was assayed against three mosquito species at various concentrations ranging from(50-450 ppm) under the laboratory conditions.The LC_(50) and LC_(90)value of the O.thymiflorus leaf extract was determined by Probit analysis.Results:The LC_(50) values of hexane,chloroform,ethyl acetate,acetone and methanol extract of O.thymiflorus third instar larvae of An.stephensi were LC_(50)= 201.39,178.76,158.06,139.22 and 118.74 ppm; Cx.quinquefasciatus were LC_(50)=228.13,209.72.183.35,163.55 and 149.96 ppm and Ae.aegypti were LC_(50)=215.65,197.91,175.05,154.80 and 137.26 ppm,respectively.Maximum larvicidal activity was observed in the methanolic extract followed by acetone,ethyl acetate chloroform and hexane extract.The larval mortality was observed after 24 h exposure.No mortality was observed in control.Conclusions:The present results suggest that the effective plant crude extracts have potential to be used as an ideal eco-friendly approach for the control of mosquito vectors.This study provides the first report on the larvicidal activity of this plant crude solvent extract of against An.stephensi,Cx.quinquefasciatus and Ae.aegypti mosquitoes. Objective: To determine the mosquito larvicidal activities of hexane, chloroform, ethyl acetate, acetone and methanol leaf extract of Orthosiphon thymiflorus (O. thymiflorus) against Anopheles stephensi (An.stephensi), Culex quinquefasciatus (Cx.quinquefasciatus) and Aedes aegypti . aegypti). Methods: The larvicidal activity was assayed against three mosquito species at various concentrations ranging from (50-450 ppm) under the laboratory conditions. LC_ (50) and LC_ (90) value of the O. thymiflorus leaf extract was determined by Probit analysis. Results: The LC_ (50) values ​​of hexane, chloroform, ethyl acetate, acetone and methanol extract of O. thymiflorus third instar larvae of An.stephensi were LC 50 = 201.39,178.76,158.06,139.22 and 118.74 ppm; Cx.quinquefasciatus were LC 50 = 228.13, 209.72.183.35, 163.55 and 149.96 ppm and Ae.aegypti were LC 50 = 215.65, 197.91, 175.05, 154.00 and 137.26 ppm, respectively. Maximum larvicidal activity was observed in the methanolic extract followed by acetone, ethyl ace tate chloroform and hexane extract.The larval mortality was observed after 24 h exposure. No mortality was observed in control. Conclusions: The present results suggest that the effective plant crude extracts have potential to be used as an ideal eco-friendly approach for the control of mosquito vectors. This study provides the first report on the larvicidal activity of this plant crude solvent extract of against An. stephensi, Cx.quinquefasciatus and Ae. aegypti mosquitoes.