A plasma-initiated degenerative transfer (DT) graft polymerization (PDTGP) was carried out on the surface of porous polypropylene membrane, with acrylic acid as monomer and iodoform as transfer agent. The polymerization rate was found to increase linearly with time. Well-defined poly(acrylic acid), with a narrow polydispersity (1.31), were obtained. Less solvent effect was observed in the PDTGP, whereas stronger solvent occurred in the plasma-initiated polymerization without iodoform. It was speculated that the unconventional radical induced by plasma should behave similarly in forming the dormant species as the conventional radical did. The polymerization is proposed to undergo via a DT mechanism. For modified membranes, graft amounts were indicated to increase linearly with conversions, i.e., proportional to molecular weights of graft chains. The PDTGP was proved a desirable method for controlling pore sizes of porous membranes.