Poly(vinyl alcohol) (PVA) membranes for ultrafiltration were fabricated by heat-treatment to separate macromolecules from microsolutes. PVA is a hydrophilic polymer with good mechanical properties because of its semicrystalline structure. The membranes were heat-treated at 100 degreesC for 1 h to increase their crystallinity and thereby their mechanical strength. The mechanical strength of the membranes was evaluated using a dynamic mechanical analyzer by measuring their compressive and tensile moduli. Membrane selectivities and protein fouling of heat-treated PVA membranes were compared to the commercial poly(ether sulfone) (PeS) and regenerated cellulose membranes. Myoglobin from horse skeletal muscle was used as a model protein, and L-tryptophan was used as a model microsolute. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to identify protein fouling on the surfaces of these membranes under flow and nonflow conditions. It was found from the selectivity and DRIFTS studies that PVA membranes were more resistant to fouling than regenerated cellulose and PeS membranes.