Response surface methodology was used to optimize spray drying process for producing biopesticide powders of Bacillus thuringiensis by using fermented broth of starch industry wastewater and wastewater sludge. Analysis of variance was carried out using number of viable spores in the powder as dependent variable. The determination coefficients of models were 92 and 94% for fermented broth of starch industry wastewater and wastewater sludge, respectively. Under the optimal conditions of the operational parameters of spray drying, the numbers of viable spores were 2.2 × 10(8) and 1.3 × 10(8) CFU/mg in the dry powders for starch industry wastewater and wastewater sludge respectively, with a loss of viable spores of 18 and 13% when compared with their respective fermented broths. The entomotoxicity (measured by the bioassay method) of the powders obtained under optimal conditions showed a loss of 28 and 18% when compared with the fermented broth of starch industry wastewater and wastewater sludge, respectively. The optimized results of spray drying were used for field application calculations. The volume of fermented broth required to produce powder formulated product when compared with the volume required for liquid formulation product in order to treat 1 ha of balsam fir was less and offered several advantages.