ST strain, isolated from yogurt purchased from a local market and identified as Streptococcus thermophilus based on physiological-biochemical characteristics and 16S rDNA sequence, produced 55.62mg·L-1 of exopolysaccharides (EPS). The EPS level produced by strain ST depended upon incubation time (24h), tem(20g·L-1). The major monosaccharide of EPS formed by this strain was confirmed to be glucose. Moreover, data from the lyophilization preparation of strain ST showed that the optimal medium containing NFMS (100.0g·L-1), yeast extract (3.0?g·L-1), CaCO3(9.0g·L-1) and whey powder (20.0g·L-1) promoted its viable cells to a level of 1.05×109CFU·mL-1. The combination of NFMS (160.0g·L-1), glycerol (30.0g·L-1), sodium glutamate (30.0g·L-1) and Tween 80 (5.0g·L-1) was proved to be a good cytoprotectant for the protection of strain ST against the stresses of freeze-drying. Temperature, pH and rotation speed were important factors for gaining high viable counts in pilot-plant production of strain ST lyophilizator. Theoptimal combination including fermentation temperature (37℃), rotation speed (90r·min-1) and pH (5.9), resulted in a direct-vat-inoculation preparation of strain ST that contained viable cells of 1.7×1011CFU·g-1 after lyophilization. Use of lyophilized strain ST preparation to directly ferment 80.0g·L-1 reconstituted skim milk to yogurt produced lower whey separation than that of yogurt made with non-EPS strains used as controls.