The impact of mixed starters consisting of Streptococcus thermophilus PZST4 and Lactobacillus bulgaricus PZLB5 in different proportions on the fermentation period of fermented milk and its acidity, texture, syneresis and flavor during storage was investigated. The results showed that viable cell ratios between Streptococcus thermophilus PZST4 and Lactobacillus bulgaricus PZLB5 had a striking effect on the quality of fermented milk, and a ratio of 50000:1 was the optimal combination based on the quality parameters tested.