Polysulfone ultrafiltration hollow fibers were chemically modified on the surfaces with propane sultone and SnCI4, and immersed in HCI solution subsequently. The immersion of the fibers in HCI solution yielded lower molecular weight cutoff of the fibers than those without the immersion. The fiber, denoted as HP‐SB‐17H, rejected 5% of raffinose at feed concentration = 0.5 wt % and 14% of NaCI at the feed concentration = 0.0025 wt %. The rejection of NaCI for HP‐SB‐17H was found to increase with the decrease of the feed concentration, and showed the tendency of Donnan exclusion. The effective fixed charge density was estimated to be 7.74 × 10−4 eq/L for the fiber. Absorption of poly(ethylene glycol) and bovine serum albumin at pH 7.0 on nonmodified and modified fibers was estimated from the ratio of Jη/J0η0, where J is flux, η is viscosity, and the suffix zero shows the values of pure water. The modified fibers with the propane sultone showed better results of antiabsorption than the nonmodified and conventionally sulfonated fibers in this study. This was attributed to the high flexibility of a sulfonated group originating from the existence of a joint segment of (‐CH2‐)3 in the modified fibers.