Abstract: In order to improve the viable count of lactic acid bacteria in koumiss powder produced by vacuum freeze- drying, 3 kinds of freeze- drying protective agents were screened by two level fractional factorial design,and the central point of response surface experiment was confirmed by the steepest ascent experiment.The optimal additions of 3 freeze-drying protective agents were 2.30%(W/V) of maltodextrin,3.50%(W/V) of trehalose and 3.10%(W/V) of α-cyclodextrin. Under the optimal conditions,the viable count of lactic acid bacteria in koumiss powder was up to(8.78±0.10)×108CFU/g.The freeze-drying koumiss powder had higher viable count of lactic acid bacteria and good flavor and quality,which could provide theoretical basis for processing of mare's milk and its' production.