The addition of L. casei AST18 improved the quantity of Lactobacillus, but the number of Streptococcus lactis in 2% AST18-added yogurt decreased by 1.0 Log (cfu/mL) compared with that in the blank group. L. casei AST18 exerted no significant influence on viscosity, water holding capacity, sensory quality, pH and titratable acidity.