Hydrophilic hollow fiber ultrafiltration membranes produced from a blend of polysulfone/poly(vinyl pyrrolidone) (PVP, K90) were post-treated with a hypochlorite solution. The results showed that the fluxes of all membranes that were treated with hypochlorite were 4.7-5.3 times higher but the rejections of the treated membranes were much lower than that of an untreated membrane. This suggests that hypochlorite treatment can alter the pore size of treated membranes while eliminating swelling of PVP in the pores. The results also showed that there was an optimum treatment time with hypochlorite to achieve a hydrophilic membrane with a high flux.