Abstract: The mass-transfer coefficient k is an important parameter for predicting the concentration polarization of reverse osmosis and other membrane separation processes. In order to determine the k value precisely, a diffusion current method with special porous electrodes has been developed. This method can be used to determine the k values for both one dimensional and two dimensional flow. It seems that the actual situation of membrane process is closely approached, so the dimensionless empirical equations obtained have a greater practical value. The equations of pre?ent work are compared with the data of previous authors. Many results seem to be in good agreement. Therefore this paper offers useful reference for research and design of diversified membrane separation systems in future.