Bacillus sphaericus 2362 containing calcium alginate microcapsules were prepared to examine the changes in viability and toxicity of the pathogenic bacterium. The effects of acidic pH and spore loading on the larvicidal activity of free and encapsulated Bacillus sphaericus 2362 were tested against Culex sp. mosquito larvae by bioassays performed in the laboratory. Results showed that encapsulation was also effective on Bacillus sphaericus 2362 spore stability. Although ultraviolet (UV) light reduced the viability of Bacillus sphaericus 2362 spores in shorter times, Bacillus sphaericus 2362-alginate microcapsules were more resistant to continuous UV exposure. Increased persistence against high temperature and several chemical materials was also observed.