In hemodiafiltration, ultrafiltration by use of a hemodiafiltration membrane in addition to dialysis is essential in order to remove medium and high molecular weight solutes. Depending on the ultrafiltration rate and the membrane parameters of solute permeability and sieving coefficient, which in turn depend on both solute and membrane properties, it was assumed that concentration polarization might arise in a hemodiafiltration system in the same way as in reverse osmosis and nanofiltration. In this study, by applying reported analysis equations to the author's former simulation model, it was confirmed that concentration polarization does occur at the blood-side boundary layer of the hemodiafiltration membrane under specific conditions of high molecular weight solute, with a conventional hemodialysis membrane operated at above a certain ultrafiltration flow rate. This result demonstrated that the simulation model based on the analysis equations used can be applied widely to separation, ranging from hemodialysis to hemodiafiltration.