A method of decolorizing and concentrating aqueous of organic dyes in an ultrafiltration process is described. The process involved poly- sulfone membranes prepared from 15% (wt.%)polysulfone solution in dimethylformamide and formed on a glass support. The experiments were carried out under static and dynamic conditions for five organic dyes of a molecular weight ranging from 327 to 1048.2. The pressure applied was 1.5 MPa. Membranes exhibiting the best properties are capable of retaining 90 to 100% of organic dyes of a molecular wieght above 700 during their work under dynamic conditions. The measured volume fluxes through these membranes ranged from 0.08 to 0.18 m 3 /m 2 day.