The effect of external recycle on the membrane dialysis with single pass in both phases on double pass in retentate phase, under parallel flow was investigated. Considerable improvement in performance is obtainable by using recycle operation to create the desirable effect of increasing the fluid velocity, which overcomes the undesirable effect of decreasing the concentration difference for mass-transfer due to the remixing at inlet. The recycle can enhance the performance of membrane dialysis, especially for higher volume flow rate or higher concentration of inlet solution. Further moer, double pass operation is more effective than the single pass because of the increase in fluid velocity, resulting in increasing the mass-transfer coefficient.