Abstract: To develop the mixed starter culture,the strains of Saccharomyces cerevisiae Y5-1 and Lactobacillus siliginis L5-1 were previously isolated from traditional natural fermented sourdough and selected as the tested strains for mixed fermentation to make sourdough,and the effects of mixed fermentation of yeast and lactic acid bacteria on the quality of steamed bread was explored.The results showed that the pH value of the two sourdough groups fermented by Lactobacillus siliginis L5-1 was significantly decreased,and the pH value could be reduced to pH3.8 after 24 hours of fermentation.The metabolites of Lactobacillus siliginis L5-1 could not affect the growth of Saccharomyces cerevisiae Y5-1.However,compared to the fermentation of Saccharomyces cerevisiae Y5-1 alone,the mixed fermentation of sourdough by the two strains could significantly improve the quality of steamed bread,including flavor,taste,texture,elasticity,etc.,and the quality of sourdough steamed bread fermented only by the strain Lactobacillus siliginis L5-1 was poor.This suggested that the strain of Lactobacillus siliginis L5-1 was not suitable for making sourdough steamed bread by fermentation alone.The Lactobacillus siliginis L5-1 can be used as a supplementary strain to interact with Saccharomyces cerevisiae Y5-1 to improve the quality of sourdough steamed bread during the fermentation process.This will provide a theoretical reference to the development of mixed starter culture of yeast and lactic acid bacteria for the industrial production of fermented flour products.