Abstract: It is critical for hydrolysates from starch by β-amylase to induce mesophilic (-amylase fermented by Bacillus subtilis.Their hydrolysates were determined by HPLC with differential refractometer detector. The results showed that the addition of heat resistant α-amylase was 5 ~ 10U /g, the level of glucose was in trace amount, 0.94% ± 0.048%, and it could not produce catabolic repression to B. subtilis. The optimal parameters of enzyme hydrolysating was β-amylase 200U /g, temperature 60℃, time 28h, and the level of maltose was 75.8% ± 1.7%.The hydrolysates from sweet potato starch by β-amylase could induce mesophilic (-amylase fermented by Bacillus subtilis.The research has important significance in theory and practice on fermentation mesophilic (-amylase by Bacillus subtilis.