The effect of hydrophilic group composition in methacrylate-based copolymer membranes on water content, the dissolved-oxygen permeation and their handling underhydrated conditions has been investigated. The methacrylate-based copolymer was synthesized by the radical bulk polymerization of monomers having hydrophobic groups, trimethylsilylmethyl methacrylate (TMS) and methyl methacrylate (MMA), with a hydrophilic group, N,N-dimethyl acrylamide (DMAA). The dissolved-oxygen permeability of these copolymer membranes was correlated to the silicon content and water content in the copolymers. The d-spacing of each hydrated membrane increased with the increase of the water content. Furthermore, we attempted heavy ion irradiation of one series of the copolymer membranes. For the heavy ion irradiation, Xe-129 ion was used in this investigation. The dissolved-oxygen permeability of the heavy ion-irradiated copolymer membranes became higher compared with that of the untreated membranes. The d-spacing and flexibility of membrane scarcely changes by heavy ion irradiation. The dissolved-oxygen permeability coefficient of a part of Xe ion-irradiated membrane exceeded the lowest desired oxygen permeability coefficient line for supplying the oxygen to cornea.