A membrane material comprises a hydrophobic and a hydrophilic polymer. The hydrophilic polymer consists of 10-50 wt% of a low molecular weight component (molecular weight <； 100,000) and 90-50 wt% of a high molecular weight component (molecular weight &ge； 100,000). The membrane material may be subjected to an insolubilization treatment to provide a permselective membrane suitable for use in dialysis. The membrane material may have an overall mass transfer coefficient (Ko), for a Stokes' radius of at least 30 ANGSTROM (as determined by a diffusion test using dextran), of &ge； 0.025 cm/min and a permeability to albumin of &le； 4%.
