Porous poly(ethylene-co-vinyl alcohol) (EVOH) membranes were prepared by polymer crystallization by the thermally induced phase separation (TIPS) process. The permeability of these membranes was examined with respect to solutes of various sizes. Higher solute rejection and lower water permeance were obtained by increasing the polymer concentration in the membrane preparation process and by increasing the cooling rate in the TIPS process. These results were discussed based on the crystalline particle sizes formed in the membranes. The membrane performances were influenced by the kinds of diluents used in the TIPS process. The membranes prepared in the EVOH/propanediol system showed a higher rejection coefficient than did those in the EVOH/butanediol system.