Efficacies of locally isolated bacterium, Bacillus sphaericus total proteins have been investigated against the 3rd instar larvae of wild mosquito Culex quinquefasciatus under the laboratory conditions.The LC50 values were recorded as 19.069 ug/ul at 72 h posttreatment. Association of both the proteins of 42 kDa and 51 kDa were found to require for mosquitocidal efficacy. The thermal stability properties of the Bin proteins were performed at various temperature ranges from 40 C, 50 C, 60 C, 70 C, 80 C & 90 C. The efficacy of the heat incubated Bin proteins were tested and showed that the binary proteins were active up to 70 C but lost their activity when treated at 80 C and 90 C. Among the two Bin proteins, 42 kDa proteins were found to be more stable than the 51 kDa protein. This data suggest that both the proteins were required for mosquitocidal efficacy for the production of bioinsectiside which would be used as a biological control of mosquito."