The activity of glucoamylase has been investigated in W/O microemulsion of cemtyltrimethyl ammonium bromide/n-pentamol/iso-ctance/water system and compared with that in aqueous solution. It was observed that the optimun temperature and pH of the enzyme decreased,and the maximum hydrolysis rate of starch(V_m)and Michaelis constant(K_m)increased nearly 6 and 3 times,respectively in microemulsion compared with that in aqueous solution.