Activity of mushroom tyrosinase was studied in three ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) and 1-butyl-3-methylimidazolium methylsulfate ([BMIm][MeSO4]), and was compared to that in chloroform. Kinetic parameters of the enzyme were determined and the results indicate that the enzyme in ionic liquids basically follows the same catalytic mechanism as in water, and that the ionic liquids may affect the enzyme activity by direct interacting with the enzyme and thus hindering the E-S binding due to their high hydrophilicity and polarity.