Abstract: The present study aimed to investigate the physicochemical properties of Lactobacillus fermentum isolated from yak yogurt (LFYY) fermented soybean milk. The artificial gastric juice survival and growth rate in bile salt of LFYY were about four and seven times higher than Lactobacillus bulgaricus (LB) . The pH of LFYY fermented soybean milk was higher than mixture bacterial strains (LM, LFYY∶LB=1∶1) fermented one, and LB fermented soybean milk showed the lowest pH after 6 and 12h fermentation. Total acidity of these fermented soybean milk showed the opposite trends with the pH. In the fermentation process at 6h and 12h, the counts of Lactobacillus in LM fermented soybean milk were more than LFYY and LM fermented soybean milk. The amino type nitrogen content and activity of isoflavones (daidzein and genistein) in LFYY fermented soybean milk were close to LB one, and more than LM one (p<0.05) . The sensory qualities of LFYY and LM fermented soybean milk were also better than LB one. From there results, LFYY fermented soybean milk showed the better qualities than LB one, the LM could increased the qualities of fermented soybean milk. Lactobacillus fermentum isolated from yak yogurt is good for fermented soybean milk produce.