Abstract: In order to reduce the water activity and keep the large number of living bacteria of Lactobacillus casei microcapsule powder which was isolated from Tibetan Kefir and can produce bile salt hydrolase,the method of orthogonal experimentsL₉(3~4)were used to investigate the dry conditions,and the effect of different spray drying techniques on the water activity of microcapsule powder and the number of the living bacteria were studied.The results showed that the amount of added Arabic gum was 40%,the air intake / outlet temperature was170 /75 ℃ and the velocity of peristaltic pump was 75 m L / min,the living bacteria number of the microcapsule powder was 2.37 × 10~9 CFU / g and the water activity was 0.096.This method not only reduced the water activity but also kept the large number of living bacteria of the microcapsule powder,which can provide the practical basis of the microencapsulation production of Lactobacillus casei.