Yogurt has many functions including inhibiting the growth of intestinal putrefying bacteria propagation,overcoming lactose intolerance,lowering cholesterol levels,and even preventing cancer and so on.Fermentation strain is the key to produce high quality yogurt.Lactobacillus bulgaricus（now renamed Lactobacillus delbrueckii subsp.bulgaricus） is one of the most common strains in yogurt fermentation process.In this paper,acid producing ability,viscosity producing ability and aroma producing ability of Lactobacillus bulgaricus was determined for further investigating fermentation characteristics of Lactobacillus bulgaricus.The results showed that the acid producing ability and viscosity producing ability of the Lactobacillus bulgaricus were strong during fermentation period,relatively weak during post-fermentation period.The aroma producing ability was strengthened gradually during post-fermentation period.