Wacker type oxidations of alkenes were performed using an [alkene \Pd-black (anode)\ H-3 PO4 \graphite (cathode)\ O-2 + NO] gas-cell at 353 K. The addition of NO to O-2 in the cathode led to a dramatic enhancement of the oxidation rate of ethylene to MeCHO more than 10 times. The kinetic experiments were studied to get information on reaction mechanisms and the optimum conditions for MeCHO synthesis. The enhancement was ascribed to the acceleration in the rate of electrochemical oxidation of Pd(0) to Pd(II) due to the formation of NO2 at the cathode. The formation of NO2 led to an increase in the electromotive force of the cell and the over potential at the Pd anode. The graphite without precious metals was sufficient as the cathode for the reduction of NO2 into NO and H2O. The electrochemical reduction of O-2 to H2O was catalyzed by NO. In the case of propene oxidation, the formation of acrolein, the major product for the [C3H6-O-2] cell, was remarkably decelerated and acetone was the major product when NO had been added to O-2. These observations may be ascribed to changes in the concentrations of Pd(O) and Pd(II) which are responsible for the pi -allyl and Wacker type oxidations, respectively.