Three types of L-phenylglycine-fixed membranes were prepared by varying casting conditions. The optical resolution of racemic phenylglycine (DL-Pgly) was performed by pressure gradient. L-Pgly-fixed membranes were permeable in preference to D-Pgly to L-Pgly, and the maximum separation factors of respective membrane under the operating conditions were 9.1, 8.6 and 2.7. Apparent self-association constants were evaluated from the dialysis data. By applying these values to the basic solute flux equations at a given pressure gradient, the values of the viscous parameters were evaluated. The ratio of viscous parameter of D-Pgly to that of L-Pgly depended on the apparent self-association constant. The separation factor was successfully represented on the basis of the basic solute flux equations including the apparent self-association constants, and the separation factor became larger in denser membranes with low volume flux.