This research focuses on Nafion modification using plasma techniques for direct methanol fuel cell applications. The results indicated the both argon (Ar) and carbon tetrafluoride (CF4) plasma treatments modified the Nafion surface substantially without altering the bulk properties. The Nafion surface exposed to CF4 plasma resulted in a more hydrophobic layer and an even lower MeOH permeability than the Ar-treated membrane. The plasma operating conditions using CF4 were optimized by utilizing an experimental design. The minimum MeOH permeability was reduced by 74%. The conductivity was 1-2×10_-3 S/cm throughout the entire experimental range. Suppressed MeOH permeability can be achieved while maintaining the proton conductivity at a satisfactory level by adjusting the plasma operating conditions.