The purpose of this study is to clarify the influence of membrane vibration on membrane rejection characteristics. The permeate flux and the apparent NaCl rejection of NaCl solutions were measured by changing the vibration amplitude of the NF membrane, and the relationship between the measurements and fluid shear rate near the vibrating membrane surface was investigated. The NaCl concentration on the membrane surface and the thickness of concentration boundary layer were also estimated, using the velocity variation method modified for the vibrating membrane separation, and the influence of membrane vibration and operating conditions on the NaCl rejection was discussed. The results showed that the apparent NaCl rejection increases with increasing the vibration amplitude, that is, with increasing the shear rate. The increase of the apparent NaCl rejection is attributed to a decrease in the thickness of concentration boundary layer with acceleration of the mixing of the solution near the vibrating membrane, and to a decrease in the concentration on the membrane surface. The apparent NaCl rejection decreases with increasing NaCl concentration in solution, while it increases with operating pressure. It was also found that the influence of the membrane vibration is strong at higher NaCl concentration and lower operating pressure.