A method of obtaining membranes with a developed inner wall structure has been worked-out by establishing appropriate spinning conditions. Obtaining a developed Surface of membranes without interference into the spinneret structure is feasible. Membranes with a developed inner Surface bear higher Ultrafiltration than that of membranes of a smooth surface made from the same membrane-forming solution. No essential differences in the molecular weight cut-off values for both types of membranes were observed. The scanning electron microscope images of membranes of developed inner surface were shown.