Effects of lipase activity regulation in ionic liquids on synthesis of starch stearate were investigated in the present study. The results showed that degree of substitution of starch stearate increased with increasing water activity and the amount of hydrated salts. When water activity reached 0.61, the amount of addition was 80%, the degree of substitution reached maximum value of 0.111. The catalytic capability of enzyme is sensitive to pH values, and the highest degree of substitution could be obtained when the lyophozyme in a buffer solution with pH 7.1,when proper additive quantity of lyophozyme was 10.4%. The lipase that lyophilized with organic compounds such as Glycine and polyethylene glycol showed higher catalytic efficiency in ionic liquids than the enzyme without any protective agent. Lipase was found working most efficiently when polyethylene glycol was used as protective agent.