The mass transfer coefficient of cylindrical baffles in an agitated vessel has been measured for the first time with the constant potential method using aqueous solution of 1 N-KOH + 0.2 N-K4Fe(CN)(6) + 0.01 NK3Fe(CN)(6) The average mass transfer coefficient on the baffles was three to five times larger than that of the vessel wall based on the power consumption per unit volume. The average mass transfer coefficient on the baffles increased with decreasing baffle diameter. The number of baffles, the clearance between the baffles and vessel wall, the position of the baffles and the position of the impeller did not affect the average mass transfer coefficient of the baffles under these experimental conditions. The average mass transfer coefficient of the cylindrical baffles measured herein agrees with the value obtained by an equation based on one published before. The distributions of the local mass transfer coefficient of the cylindrical baffles are shown graphically for various impeller speeds. The local mass transfer coefficient of the baffles near the impeller was larger than those in other positions, and that near the liquid free surface increased up to the same level as that of the baffles near the impeller as the impeller speed increased.