Polyethersulfone membranes were prepared from quaternary systems containing N,N-dimethylacetamide (DMAc) as solvent, polyvinylpyrrolidone (PVP) as constant additive and acetic acid, acetone and water as variable additives. Phase inversion via immersion precipitation was employed for manufacturing of membranes. The prepared films were immersed in the mixture of pure water and 2-propanol (30/70 vol%) as the non-solvent. Acetic acid caused an increment in the flux at high polymer concentration (16wt%) and a decline in the flux at low polymer concentrations (10 wt% and 13 wt%). Acetone and water as the solvent in the casting solution declined the flux at any polymer concentration tested. The morphology and performance of the prepared membranes were investigated by scanning electron microscopy and separation experiments using milk as the feed.