In this work, polyethersulfone (PES) asymmetric nanofiltration (NF) membranes were prepared by immersion precipitation phase inversion process. The casting solution contained N-methyl-2-pyrrolidone (NMP) as solvent, 1-propanol and 2-propanol as nonsolvent additives, and polyvinylpyrrolidone (PVP) as pore former additive. Water was used as a coagulant. The effects of the PVP content in the casting solution and the exposed time on the performances of the NF membranes were investigated. It was found that with the increase of PVP content, the pure water flux (PWF) increased to the largest value and then decreased. The rejection to PEG 1000 always decreased. The largest value (1281.40kg center dot m-2 center dot h-1 center dot MPa-1) of PWF appeared when the content of 1-propanol was 9wt.%. However, when 2-propanol was added in the casting solution, the largest value of PWF was only 678.37kg center dot m-2 center dot h-1 center dot MPa-1 (the content of 2-propanol was 7 wt.% and other preparing conditions were unchanged). The results meant that both PWF and rejection of the membranes with 1-propanol as additive were higher than that of 2-propanol as additive. The possible reason was discussed from the viewpoint of the difference of solubility of propanols to PES and PVP.