Membranes were prepared from solutions containing Udel-type polysulfone (PSf) and sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (SPPO). Polymer solutions in 1-methyl-2-pyrrolidone were cast on a nonwoven textile and precipitated in a water bath. The permeabilities and selectivities of the prepared membranes depended on the concentrations of both polymers in the casting solution. The higher the concentration of PSf, the lower were the permeabilities to water and average pore sizes of the membranes. On the other hand, a very small amount of SPPO in the casting solution (about 1-4 wt % relative to the casting solution weight:) brought about a considerable increase in water permeabilities and had a small influence on the average pore sizes. The effects were most pronounced if SPPO with a degree of sulfonation of 20-40% was used. The considerable increase in water permeabilities was explained by separation of the PSf and SPPO phases during precipitation in water and by the concentration of hydrophilic SPPO on the surface of the membrane and its pores. The determinations of the oriented concentration potentials proved the presence of a negative surface charge in the membranes.