Asymmetric ultrafiltration (UF) membranes were prepared from locally made wholly aromatic polyethersulfone (PES) polymer, similar to Vitrex type, using aprotic solvents and organic additives by phase inversion method. The effect of nature of additive, solvent, ambient humidity during membrane casting and gelling medium on membrane performance were studied. The membranes were characterized in terms of separation behaviour far polyethylene glycol-5000 solute, molecular weight cut off (MWCO) profile and direct electron microscopic observations. The performance of UF membranes for sodium sulfate, rhodamine-B dye and oligomers of starch hydrolyzate are reported as a function of pressure.