Hollow fiber membranes were prepared by thermally induced phase separation from three types of polyvinyl butyral (PVB) and a blend of two of these polymers. Although the difference in the chemical composition of the PVB polymers used was not remarkable, their respective membrane performances were quite different. With a high phase separation temperature the pore size of the prepared membrane was large, because structure growth occurred for a long time. Water permeability tests of the wet membranes showed the results that corresponded to the pore sizes of the membranes. By contrast, the results for the dried membrane appeared to be related to the hydrophilicity of the PVB polymer and independent of pore size in the wet condition. Although the membrane with high wettability had low mechanical strength, the membrane from the polymer blend of two different PVB polymers showed adequate wettability and mechanical strength. This produced a hollow fiber membrane with favorable characteristics for application in water treatment. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013