Objective:To evaluate aqueous and ethanol extract of Cassia didymobotrya leaves against immature stages of Culex quinquefasciatus.Methods:The mortality rate of immature mosquitoes was tested in wide and narrow range concentration of the plant extract based on WHO standard protocol.The wide range concentration tested in the present study was 10 000,1 000,100,10 and1 mg/L and narrow range concentration was 50,100,150,200 and 250 mg/L.Results:2nd instar larvae exposed to 100 mg/L and above concentration of ethanol extract showed 100%mortality.Remaining stages such as 3rd,4th and pupa,100%mortality was observed at 1 000 mg/L and above concentration after 24 h exposure period.In aqueous extract all the stages 100%mortality was recorded at 1000 mg/L and above concentration.In narrow range concentration 2nd instar larvae 100%mortality was observed at 150 mg/L and above concentration of ethanol extract.The remaining stages 100%mortality was recorded at 250 mg/L.In aqueous extract all the tested immature stages 100%mortality was observed at 250 mg/L concentration after 24 h exposure period.The results clearly indicate that the rale of mortality was based dose of the plant extract and stage of the mosquitoes.Conclusions:From this study it is confirmed and concluded that Cassia didymobotrya is having active principle which is responsible for controlling Culex quinquefasciatus.The isolation of biouctive molecules and development of simple formulation technique is important for large scale implementation. Objective: To evaluate aqueous and ethanol extract of Cassia didymobotrya leaves against immature stages of Culex quinquefasciatus. Methods: The mortality rate of immature mosquitoes was tested in wide and narrow range concentration of the plant extract based on WHO standard protocol. Wide area concentration in the present study was 10 000,1 000,100,10 and 1 mg / L and narrow range concentration was 50,100,150,200 and 250 mg / L. Results: 2nd instar larvae exposed to 100 mg / L and above concentration of ethanol extract showed 100% mortality. Remaining stages such as 3rd, 4th and pupa, 100% mortality was observed at 1 000 mg / L and above concentration after 24 h exposure period. In aqueous extract all the stages 100% mortality was recorded at 1000 mg / L and above concentration. In narrow range concentration 2nd instar larvae 100% mortality was observed at 150 mg / L and above concentration of ethanol extract.The remaining stages 100% mortality was recorded at 250 mg / L. In aqueous extract all the teste d immature stages 100% mortality was observed at 250 mg / L concentration after 24 h exposure period. The results clearly indicate that the rale of mortality was based dose of the plant extract and stage of the mosquitoes. Conclusions: From this study it is is confirmed and concluded that Cassia didymobotrya has active principle which is responsible for controlling Culex quinquefasciatus. The isolation of biouctive molecules and development of simple formulation technique is important for large scale implementation.