In this study, microencapsulation by spray drying was performed to protect spores and crystals of an indigenous isolate of Bacillus thuringiensis Se13 from environmental stress. The effects of wall material, inlet temperature, and outlet temperature on microencapsulation of Bt-Se13 were investigated using Taguchi's orthogonal array. The most suitable wall material determined as maltodextrin DE10. The optimum inlet and outlet temperatures of spray drier were determined as 160 degrees C and 70 degrees C, respectively. The number of viable spores, mean particle size, wetting time, percentage of suspensibility and moisture content of the product produced under optimum conditions were determined as 8.1x10(11)cfu g(-1), 13.462 mu m, 25.22s, 77.66% and 7.29%, respectively. As a result of efficiency studies on Spodoptera exigua in the laboratory conditions, the LC50 was determined as 1.6x10(4)cfu mL(-1). Microencapsulated Bt-Se13 based bio-pesticide may be registered for the control of S. exigua and can be tested against other lepidopterans which share the same environment.