Composite membranes were prepared by plasma-induced graft polymerization of vinyl monomers onto porous substrates of high density polyethylene, and the relationship between the polymerization conditions and morphological structure and pervaporation performance toward benzene/cyclohexane mixtures was investigated in detail. The morphological structures of the plasma-grafted membranes depended on the monomer reactivity, plasma treatment manner, and graft polymerization conditions. Pervaporation properties were closely related to the graft monomers and the morphological structures. The poly(glycidyl methacrylate)-grafted membranes prepared by homogeneous both sides plasma treatment and under mild polymerization conditions showed the highest pervaporation performance with a permeation flux of 0.3 kg/(m(2) h) and separation factor of 22 at 60 wt % benzene and 70 degrees C.