In this study, methacrylic acid (MAA) was grafted onto a poly(tetrafluoroethylene) (PTFE) plate by the oxygen plasma treatment and subsequent photografting. The surfaces of the grafted PTFE plates prepared at shorter plasma treatment times and/or at lower monomer concentrations were modified hydrophilic at lower grafted amounts. Water absorptivity of the grafted layer increased with the grafted amount and the grafted layers formed at lower monomer concentrations possessed higher water absorptivity. For grafted PTFE plates prepared at the monomer concentration of 1.5 and 2.0 M after the plasma treatment, the substrate breaking occurred. The grafted amount at substrate breaking decreased with a decrease in the plasma treatment time, indicating that the location of photografting was restricted to the outer surface region at shorter plasma treatment times. It was made clear that the combination of the oxygen plasma treatment with the photografting of MAA was an effective procedure to modify the PTFE surface.