Aiming at recovering carnitine from cheese whey by using loose reverse osmosis membranes, rejection characteristics of several components in the whey were examined by using model solutions. An electroneutral membrane was found to be most effective for the separation. The rejection of carnitine was above 0.95 independent of the pH of solutions, while monovalent metal ions shelved low rejections of 0.1-0.3. On the other hand, the rejections of divalent metal ions decreased with increase of the pH, and reached a minimum of about 0.5. As a result, mono- and divalent metal ions could be removed simultaneously by adjusting the pH of the feed solutions. To clarify the effect of pH on the rejection, the permeate of MgCl2 aqueous solution was examined. The rejections of MgCl2 were greatly affected by the pH and showed the same tendency as the mixed solution. The effect of the pH on permeation of electrolyte was considered to be caused mainly by the adsorption of ions on the membrane.