The integrally skinned polyetherimide (PEI) asymmetric nanofiltration (NF) membranes were developed by the dry/wet phase inversion methods from the casting solution containing N-methyl-2-pyrrolidone (NMP) as a solvent, diethylene glycol dimethyl ether (DGDE) as a weak nonsolvent additive and acetic acid (AA) as a strong nonsolvent additive. Water was used as a coagulant. The effects of nonsolvent additives on the membrane performance were investigated. Moreover, both the membrane performance and the membrane structures were correlated. In order to find the appropriate membrane performance, nonsolvent additives were combined. We could develop the high performance NF membrane having moderate pure water flux (1.27 ton/m(2) per day) and high rejection rate (PEG 600, 83%).