The study was concerned primarily with characterization of the NF45 membrane. Its pure water permeability, the mass transfer coefficient of NaCl, and the mean radius of the membrane pores were determined. Experiments run with five pure dye solutions and an industrial dye pulp solution confirmed the potential of nanofiltration membrane separation for the treatment of textile dye plant effluent. The effects of such significant parameters as initial solution concentration, transmembrane pressure, and type of dye on two fundamental characteristics of nanofiltration (flux and separation factor) were studied.