Abstract: In order to study the role of supercritical CO₂ as a nonaqueous medium in the engineering of biochemical reactions, it is necessary to probe the effects of supercritical CO₂ treatment on microbial activity. Lactobacillus was selected as testing target, and the effects of different supercritical CO₂ treatment on the microbial activity including growth curve, the ability of osmotolerant, the ability of aciduricity, the inhibition ability and the ability of cholesterol-degrading were researched. Results show that when pressure is raised or treatment time is extended, the parameters of microbial activity happen some alterations as follows: The maximum cell concentration fall, meanwhile the growth velocity of each group of germs do not share too much differences. The ability of osmotolerant and aciduricity of germs decrease. The inhibition zones of each group are all obvious, but the diameters reduce. The average rate of cholesterol-degrading is restrained, and the effects which is made by germs treated with long time are greater than those made by germs treated with high pressure. Consequently certain measures which make up for these influences sould be studied to apply in the engineering.