Partial oxidation of ethylene with a gas-cell system were studied at 353 K. The gas-cell structure was [C2H4, H2O \ (Pd-black + VGCF)-anode \H3PO4/silica-wool \ cathode \O-2] (VGCF: vapor growing carbon fiber). Addition of NO to O-2 stream at the cathode dramatically enhanced the oxidation rate of ethylene to MeCHO more than 10 times with high selectivities > 95%. The enhancement of the formation rate of MeCHO was due to the acceleration of the electrochemical oxidation rate of Pd-0 to Pd2+ at the anode by a strong oxidant of NO2 produced from O-2 and NO. NO2 was electrochemically reduced to H2O and NO that functioned as a mediator over the graphite-cathode. When a membrane of carbon matrix holding H3PO4 was chosen instead of H3PO4/silica-wool, both H+ and e(-) could conduct from anode to cathode side through the H3PO4/carbon matrix, self-short circuiting condition. The oxidation Of C2H4 could perform with the self-shorted cell reactor excluded electric parts. Several carbon matrices were tested for the oxidation by the self-shorted cell and the suitable one was a sheet of (VGCF + AC + PTFE) (AC: active carbon) prepared by the hot-press method. This self-shorted gas-cell was more active than the cell system. In the case of propene oxidation, acetone was selectively produced with the self-shorted cell. Kinetic studies were carried out to get information for reaction mechanism of the alkene oxidation. The self-shorted cell works as a new type of membrane catalytic system for the oxidation of alkene [alkeneloxidation catalyst \ mixed conductor of H+ and e(-) \ reduction catalyst \ oxidant]. This membrane catalyst also functioned as a hydrogen permeation membrane.