Sulfonated polysulfone (SPSF) flat ultrafiltration membranes were successfully prepared by immersion precipitation phase inversion method. N-Methyl pyrrolidone was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a polymeric additive in the casting solution. The effects of casting solution formulation and preparation conditions on membrane structure and properties were investigated in present study, and the morphology of the membranes was analyzed by scanning electron microscopy. The results indicated that the performances of SPSF membranes made by chemical modification were better than polysulfone membrane. The SPSF concentration played a vital role in restricting the pure water flux (PWF), promoting the rejection coefficient, and improving the hydrophilicity. A maximum PWF and minimum egg albumin rejection coefficient were obtained when the PVP content was 10%. When the coagulation bath temperature was set to 25 degrees C, the PWF reached 480 Lm(-2)h(-1) and the ovalbumin rejection coefficient reached 92%. Longer evaporation times improved the PWF. Specifically, when the evaporation time was 70 s, the comprehensive performance was good. POLYM. ENG. SCI., 55:1003-1011, 2015. (c) 2014 Society of Plastics Engineers