To develop highly efficient proton exchange membranes (PEMs), a series of partially sulfonated and crosslinked copolymers, i.e., poly(ethylene glycol dimethylmethacrylate-co-styrene sulfonic acid) (P(EGDMA-SSA)) and poly(diethylene glycol dimethylmethacrylate-co-styrene sulfonic acid) (P(DEGDMA-SSA)), were synthesized using radical copolymerization. The compositions of the copolymers were quantified using proton nuclear magnetic resonance. The proton conductivities, methanol and water uptakes, and methanol permeabilities of the PEMs prepared from these copolymers increased as SSA content increased. The proton conductivities and uptakes of both copolymers increased abruptly when the copolymers contained >15 mol% SSA. When the P(EGDMA-SSA) and P(DEGDMA-SSA) copolymers contained the same mol% SSA, the methanol permeabilities and uptakes of the former were lower than those of the latter, while the former exhibited better proton conductivity. The PEM prepared from P(EGDMA-SSA) copolymer containing >30 mol% SSA exhibited better proton conductivity and lower methanol permeability than Nafion 117. Furthermore, these membranes exhibited considerably thermal, hydrolytic, and oxidative stabilities. Consequently, PEMs, especially those desirable for use in direct methanol fuel cells, could be fabricated from P(EGDMA-SSA) copolymers and are appealing alternatives for Nafion membranes under mild conditions.