Due to the hydrophobicity of poly(vinyl chloride) (PVC), the application of PVC membranes has been limited. In this paper, poly(vinyl butyral) (PVB) was introduced as the second polymer component to hydrophilized PVC ultrafiltration membranes. The miscibility of PVC/PVB blends in N,N-dimethyl acetamide were characterized by the solubility parameter, glass transition temperature of the blended membrane, casting solution viscosity, etc. The results showed that the PVC/PVB blended system was partially miscible at a certain proportion range. Water flux and hydrophilicity of the blended membranes were much better than that of the membranes made from pure PVC or PVB. A cross section of pure PVB and PVC/PVB blended membranes present an asymmetric finger-like structure, and the wall of the finger-like pore had a sponge-like structure. The addition of PVB could improve the hydrophilic property of PVC membranes, and the addition of PVC could increase the pore diameter at the bottom of PVB membranes.