Ultrafiltration separation of an anionic surface active agent belonging to the alkylsulfonate family was studied. Asymmetric membranes made of polyethersulfone, polysulfone, regenerated cellulose, cellulose acetate and polyamide with a molecular weight cut-off equal to 5, 10 and 3 0 kDa were used. The temperature of tested solutions ranged from 25 degrees C to 55 degrees C. The CMC value of sodium dodecyl sulfate (SDS) at different temperatures was determined by conductivity measurements. The influence of polymer material, membrane cut-off and surface active agent concentration on transport and separation properties of UF membranes under different temperature conditions was investigated. It was found that the SDS separation efficiency was influenced by membrane material. The membranes with the best separation characteristics were made of polysulfone and polyethersulfone. Deterioration in separation and transport properties of UF membranes with an increase of SDS concentration was observed. The temperature increase of SDS solutions resulted in a small reduction of the SDS retention coefficient. The permeate flux increased with temperature rise due to the solution viscosity decrease and thermal expansion of the membrane material.