Microporous hollow fiber membranes were prepared via thermally induced phase separation process by using the vessel-type melt spinning apparatus. Polypropylene which has good thermal and chemical resistance was used as a membrane material, and soybean oil and dioctylphthalate were used as diluents. Effects of operating parameters were examined on the structure variation of the membrane. As the coagulation bath temperature increased, the fiber melt underwent the slow cooling to have the residence time long enough for liquid-liquid phase separation to result in the cellular structure. The fast cooled one has spherulitic lacy structure, since polymer crystallization inhibited the liquid-liquid phase separation. The membrane with cellular structure has greater pore size and flux than the one with spherulitic lacy structure. The more miscible coagulant with diluent extracted some of the diluent from the outer surface of the hollow fiber to make the more porous surface, but has little effect on the inner surface. It was confirmed that polypropylene membrane made via thermally induced phase separation process had better thermal and chemical resistance than the commercial polysulfone and cellulose acetate membranes.