Abstract: A novel lactase-producing bacterium RY237 was selected based on β-galactosidase activity using lactose as sole carbon media, and was identified as Bacillus coagulans RY327. The activity of lactase reached 4.98 U/m L. The optimum temperature and optimum p H of β-galactosidase were 50 ℃ and 6.0, respectively. The enzyme was stable at p H5.5 ~ 8.0, with peak activity at p H7.0, and it was also stable at 40⁵0 ℃. The activity of β-galactosidase was inhibited by Ca²⁺, K+, Zn²⁺, Mn²⁺, Na+, Mg²⁺and completely inhibited by Cu²⁺. Its activity was promoted by ethylene diamine tetraacetic acid ( EDTA) .The high activity, thermostability and p H-stability make this enzyme potentially useful in dairy industry.