Suspensions of a microparticulate Lewatit ion-exchanger can be effectivelly concentrated by microfiltration (MF) to relatively high concentrations of about 25% of dry particles. This is important for formation of a hybrid process combining ion-exchange and MF. A tubular ceramic membrane with the mean pore size of 0.1 mu m and the ground ion-exchanger Lewatit S100 with the mean particle size 5.25 mu m have been used. Analysis of the flux decline revealed that the dominant membrane fouling mechanism is cake formation. With increasing suspension velocity the permeate flux significantly increases. The velocity of suspension above 2 m center dot s(-1) should be used to achieve a reasonable flux. The limiting flux was reached at a pressure of about 100 kPa, but at higher suspension concentrations even at about 60 kPa. Surprisingly, the dependence of the permeate flux vs. suspension concentration goes through a flat maximum at the mass fraction of the dry resin of about 0.13. This can be interpreted as a result of inertial lift of larger particles in the suspension. At higher ion-exchanger concentrations further accumulation of particles in the cake increases its resistance and decreases the flux. Even at concentrations as high as 37.5 mass% of wet (25% of dry) particles in the suspension the permeate flux of about 72 dm(-3) center dot m(-2) center dot h(-1) can be achieved.