The bio-efficacy of Solanum xanthocarpum leaf extract and bacterial insecticide, Bacillus thuringiensis, were assessed against the first to fourth instar larvae and pupae of Culex quinquefasciatus, under the laboratory conditions. The medicinal plants were collected from the outskirt Bharathiar University, Coimbatore, Tamil Nadu, India. The shade dried plant materials were extracted by employing the Soxhlet apparatus with ethanol (organic solvent) for 8 h and filtered. The extracts were concentrated at reduced temperature on a rotary evaporator and stored at a temperature of 4°C. Both S. xanthocarpum and B. thuringiensis show varied degree of larvicidal and pupicidal activity against various stages of C. quinquefasciatus. The LC(50) and LC(90) of S. xanthocarpum against the first to fourth instar larvae and pupae were 155.29, 198.32, 271.12, 377.44, and 448.41 ppm and 687.14, 913.10, 1,011.89, 1,058.85, and 1,141.65 ppm, respectively. On the other hand, the LC(50) values of B. thuringiensis against the first to fourth instar larvae and pupae were 133.88, 157.14, 179.44, 206.80, and 240.74 ppm; the LC(90) values were 321.04, 346.89, 388.86, 430.95, and 492.70 ppm, respectively. However, the combined treatment of S. xanthocarpum + B. thuringiensis (1:2) material shows highest larvicidal and pupicidal activity of the LC(50) values 126.81, 137.62, 169.14, 238.27, and 316.02 ppm and the LC(90) values 476.36, 613.49, 705.29, 887.85, and 1,041.73 ppm against C. quinquefasciatus in all the tested concentrations than the individuals and clearly established that there is a substantial amount of synergist act. Therefore, the present investigation clearly exhibit that both S. xanthocarpum and B. thuringiensis materials could serve as a potential of highest mortality rate against the mosquito larvae laboratory as well as the field conditions. Since C. quinquefasciatus is a ditch breeder vector mosquito, this is a user and eco-friendly biopesticide for the control of mosquito vector management program.