Poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber ultrafiltration (UF) membranes were made by using a dry-jet wet spinning process. The influences of poly(vinyl pyrrolidone) (PVP) additive on thermodynamic and rheological variation of the casting system, the morphology and the performance of membranes were investigated. The results showed that the addition of PVP in the casting solution changed the thermodynamics balance and viscosity of casting system. The retention for bovine serum albumin (BSA) of the membrane decreased with the concentration of PVP. The flux showed a non-linear relationship with the concentration of PVP, and the flux reached the maximum value of 361 Lm(-2) h(-1). When the concentration of PVP was at 2 wt%. The effects of the following hypochlorite treatment on the morphology and the performance of membranes were also evaluated. The hypochlorite treatment altered the morphology and the performance of PPESK UF membranes by leaching of PVP from the membrane. The results showed that the flux of treated membrane was improved 15% than untreated one. (C) 2007 Elsevier B.V. All rights reserved.