Thermally induced phase separation of an isotactic polypropylene-camphene solution is performed to form tubular membranes. Microscopic observation indicates that the membrane is composed of spherical clusters, a leafy structure, and a cellular structure. Wide angle X-ray scattering reveals that the crystalline regions are basically of smectic form, with alpha -form crystal formation favored at a lower molecular weight and higher concentration. The crystallinity, as measured with differential scanning calorimetry, ranges between 32 and 43% by mass for these membranes. Permeation performance, including hydraulic permeability and retention of dextran, is also determined. Experimental results indicate that hydraulic permeability increases with increasing quenching temperature. The retention is higher for membranes resulting from higher concentration and higher molecular weight polymers, quenched at a lower temperature. Statistical analysis indicates that the quenching temperature affects hydraulic permeability and retention the most, while polymer concentration affects the crystallinity of the membrane the most.