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Objective:To explore the larvicidal activity ofCatharanthus roseus(C. roseus) leaf extract and Bacillus thuringiensis(B. thuringiensis) against the malarial vectorAnopheles stephensi(An. stephensi), when being used alone or together.Methods:The larvicidal activity was assayed at various concentrations under the laboratory and field conditions.TheLC50 andLC90 values of theC. roseus leaf extract were determined by probit analysis.Results:The plant extract showed larvicidal effects after24 h of exposure;however, the highest larval mortality was found in the petroleum ether extract ofC. roseus against the first to fourth instars larvae withLC50=3.34,4.48, 5.90 and8.17 g/L, respectively;B. thuringiensis against the first to fourth instars larvae with LC50=1.72,1.93,2.17 and2.42 g/L, respectively; and the combined treatment withLC50=2.18,2.41, 2.76 and3.22 g/L, respectively.No mortality was observed in the control.Conclusions:The petroleum ether extract ofC. roseus extract andB. thuringiensis have potential to be used as ideal eco-friendly agents for the control ofAn. stephensi in vector control programs.The combined treatment with this plant crude extract and bacterial toxin has better larvicidal efficacy against An. stephensi.