Polyvinylidine fluoride (PVDF) and polyacrylonitrile (PAN) were dissolved at various ratios in dimethylformamide (DMF) and cast into membranes via the phase inversion technique. The morphology and structure of PAN/PVDF membranes were examined using scanning electron microscope (SEM), and the contact angle, equilibrium water content (EWC), porosity, and mechanical properties were also determined. The permeation performance evaluated included hydraulic permeability, degree of retention (R%), and hydraulic permeabilities (L-p). The results show that although the tensile strength of blend membrane is lower than that of PAN membrane, the elongation of blend membrane is higher than that of PAN membrane. With increasing PVDF content, the L-p of the blend membrane increased while the R% decreased. The molecular weight cut-off (MWCO) increased with the PVDF content, and ranged between 50 and 1500 kDa. In addition, the permeability coefficient of the blend membrane increased with the hydrophilicity. By blending PVDF into PAN, the MWCO of the membrane can be varied in a wide range for various applications. (C) 2003 Elsevier B.V. All rights reserved.