Porous poly(ethylene-co-vinyl alcohol) (EVOH) membranes were prepared via thermally induced phase separation. The effect of the EVOH ethylene content on the membrane morphology and solute rejection property was investigated. For EVOHs with ethylene contents of 27-44 mol %, polymer crystallization (solid-liquid phase separation) occurred, and the membrane morphology was the particulate structure. However, the liquid-liquid phase separation occurred before crystallization for EVOH with a 60 mol % ethylene content. Cellular pores were formed in this membrane. For the particulate membranes, higher solute rejection and lower water permeance were obtained for EVOH with a lower ethylene content. The membrane formed by the liquid-liquid phase separation showed a sharper solute rejection change with a change in the solute radius than the particulate membranes did.