The effect of compressed CO2 on the specific activity of chloroperoxidase (CPO) to catalyze the chlorination of 1,3-dihydroxybenzene in cetyltrimethylammonium chloride (CTAC)/H2O/octane/pentanol reverse micellar solution was studied. The results show that the specific activity of the enzyme can be enhanced significantly by compressed CO2, and the specific activity can be tuned continuously by changing pressure. The mechanism for the specific activity enhancement of the enzyme by CO2 was also studied. We believe that compressed CO2 can be utilized to tune some other enzyme catalytic reactions in different reverse micellar systems with potential advantages.