The physicochemical and sensory characteristics of soy yogurt fermented with Bifidobacterium breve K-110, Streptococcus thermophilus 3781, or Lactobacillus acidophilus Q509011 for 36 hr at $37^{circ}C$ were investigated and the soyasaponin metabolites of soy yogurt were measured. L. acidophilus reduced the pH of soy yogurt on day 0 to optimum level. After 36 hr, the Brix dropped to 8.48-$9.12^{circ}Bx$. The viable cell counts of soy yogurts on day 0 were 8.43 to 9.01 log CFU/mL. Among starters, B. breve alone produced soyasapogenol B, although it was not detected in non-fermented soybean. B. breve produced poor sensory scores in all sensory aspects. By mixing B. breve with S. thermophilus and L. acidophilus, the sensory scores of B. breve could be improved. These findings suggest that the mixed culture of S. thermopilus or L. acidophilus with B. breve may be an ideal starter for the preparation of soy yogurt.