The effect of 1-alkyl-3-methylimidazolium ionic liquids (ILs) on the hydrolysis activityof Candida rugosa lipase (CRL) toward triacylglycerol was investigated. The critical micelle concentrations (CMC) of ILs with Br - , Cl - , and [BF 4 ] - anions and the solubility of ILs with [PF 6 ] - anions were determined in phosphate buffer. Results suggested that the content of the ILs, not kosmotropicity, highly influenced the effects of anions and cations of ILs on CRL activity. As the length of alkyl chain of the cation [C n MIM] + increased, lower IL content was required to achieve high enzyme activity. Once the concentrations of the ILs with Br - , Cl - , and [BF 4 ] - anions exceeded the CMC value, enzyme activity was suppressed. The positive promotion effect of anions on enzyme activity was in the order of Br - Cl - [BF 4 ] - [PF 6 ] - . The effect of ionic liquid on enzyme activity was highly dependent on the pH and temperature of the system, with the optimum pH being 7.000. Under optimal conditions of pH 7.000, 30 o C, and 47.6 mmol/L of [C 8 MIM]Br, the highest relative activity of CRL (1734%) was achieved, with a specific activity of 54.4 U/mg protein.