The effect of convective flow on the current efficiency of an ion-selective membrane is investigated by solving the general Nern-Plank equation simultaneously with Poission equation. We found that assuming Donn equilibrium at liquid-mebrane interfaces leads to a positive deviation in the current efficiency of a membrane. The qualitative behavior of the membrane remains the same, however, regardless of whether this condition is assumed. For a fixed electrical potential drop across a membrane, the current efficiency increases with the applied current density. It is interesting to observe that, for a fixed applied current density, the higher the electrical potential drop the lower the current efficiency. If the electric Peclet number is small, the current efficiency is mainly controlled by the electrical potential drop, and if it is large, the current efficiency is controlled by the pressure drop across the membrane. It is found that the larger the electric Peclet number the more serious the concentration polarization near liquid-membrane interfaces.