The authors have investigated the surface properties which are electric conductivity, wettability, the rate constant of H₂O₂ decomposition, and surface functional groups of surface modified poly (vinyl chloride) carbon (PVCC) by cold CF4 plasma. This paper also describes the relations between the surface properties and the electrochemical behavior in an aqueous KOH solution of the gas diffusion electrodes with the plasma processed PVCC. The results are as follows: i) The conductivity of PVCC decreased with processing time. ii) The PVCC surface changed from hydrophilic to hydrophobic. iii) The PVCC with high H₂O₂ decomposition ability was obtained by the plasma processing. These facts would be explained by the increase of fluorine-containing functional groups on PVCC surface. The polarization and discharge characteristics of oxygen electrode with PVCC were much improved by the plasma processing. These can be explained by the formation of the stable three phase zone owing to moderate water repellency, the high H₂O₂ decomposition ability, and the developed fine pore structure of the plasma modified PVCC electrode.