Polysulfone ultrafiltration hollow fibers were chemically modified on the surfaces with propylene oxide and Friedel-Crafts catalysts. A peak at 1.6 ppm was observed in H1-NMR spectrum of the modified fibers at 45°C, while the peak was not observed at 27°C measurements. The peak was attributed to a hydroxide group from the peak shift at high temperature. Micro ATR spectra of the modified fibers also suggested existence of CH(CH3)CH2OH segments on those surfaces. The modified fibers showed 10–80% rejection of polyethylene glycol 6000 at feed concentration of 0.5 wt %, depending on the conditions of surface reaction, and were found to have smaller molecular cut-off than nonmodified fibers. The fibers were also compared with modified fibers with propane sultone reported previously [A. Higuchi et al., J. Appl. Polym. Sci., 36, 1753 (1988)], which had negatively charged segments of CH2CH2CH2SO. Absorption of bovine serum albumin on the modified fibers was estimated to be less than the nonmodified fibers from permeation measurements. It is suggested that fibers having hydrophilic surfaces show better results of anti-absorption of solutes than the nonmodified fibers.