Polyethylene (PE) microfiltration films and composite nanofiltration membranes on their base have been elaborated. Microporous films are formed by melt extrusion process of linear PE without any heterogeneous admixtures. PE membranes of 10-15 microns in thickness are characterized by a large number of through flow channels with 0.01-0.50 mu m in size, overall porosity 40-50%, mean size of pores is 0.045 microns. Specific properties of relief-like surface of PE membranes provide a very high adhesion of these films to any coatings. Composite membranes were prepared by deposition of polyacrylonitrile (PAN) layers onto the surface of PE films. Phase inversion method was used to form PAN layer. As a result the initial microporous hydrophobic film transforms into hydrophilic ultra-filtration and nanofiltration membrane. Polymer concentration of the casting solution has been varied. The preparation of composite membranes by phase inversion gives a possibility to form PAN layers onto PE porous films for effective cut-off of bovine serum albumin (BSA).