Thermally-induced molecular graft copolymerization of 4-vinylpyridine (4VP) with the ozone-preactivated poly(vinylidene fluoride) (PVDF) was carried out in N-methyl-2-pyrrolidone (NMP) solution to produce the 4VP-g-PVDF copolymer. The resulting 4VP-g-PVDF copolymers with different graft concentrations of the base polymer side chains were cast into microfiltration (MF) membranes by phase inversion. When compared to the MF membranes prepared from PVDF with grafted acrylic acid (AAc) polymer side chains from the earlier work, the 4VP-g-PVDF MF membranes also exhibited pH-sensitive permeability to aqueous solutions, but in an opposite manner. The fabrication of membranes from functional graft copolymers represented a relatively simple and effective approach to the preparation of membranes with well-controlled pore size, uniform surface, and pore-surface composition, and pH-sensitive flux properties.