Ultrasound was irradiated during solutes permeation through a dialysis membrane. Since a power ultrasound leads to cavitation which can damage the membrane structure, cavitation-free condition was carefully selected. Applying ultrasound increased a few tens percent of steady-state permeation rate. Furthermore, a sudden increase or decrease of the solute concentration on the receiving side was observed. Such a stepwise concentration change is partly explained from the thinning and developing of liquid film adjacent to the membrane surface with and without applying ultrasound. Effects of ultrasound on solute trasnfer were reversible and no damage of the membrane structure was found by SEM observation. Moreover, the liquid flow near the membrane surface was visualized with and without ultrasound. Under a slower flow situation, standing wave was formed in the vicinity of the membrane, and the solute permeation was enhanced by ultrasonic irradiation. While under a faster flow, the standing wave was disturbed and no enhancement was observed for the solute permeation. Moreover, ultrasonically enhanced mass transfer coefficient for slower flow was bigger than that for faster flow. This fact implies that the standing wave adjacent to the membrane surface closely relates with the enhancement of solute permeation through the membrane.