In this research,we studied the effect of the fermentation conditions on the acidity,viscosity and the viability of Lactobacillus of soya-yogurt using fresh soybean and finished milk as raw material.The results showed it was feasible to produce soya-yogurt from soy-bean milk using traditional yogurt starter.Experimental factors and levels were determined by single-factor experiments.The orthogonal experimental design was used to optimize the fermentation conditions.The results showed that the optimal fermentation conditions were as followes: ratio of soy-bean milk to milk was 5∶ 5,fermentation time was 9h,inoculation volume of taming lactobacillus was 0.5 g/L.In these fermentation conditions,products obtained good acidity value of more than 70°T and moderate viscosity value of 2025 mPa·s.The yoghurt had good texture and fermented flavor,and had no soybean pungent taste.