The effects of experimental variables for the electrochemical reduction of carbon dioxide by Carbon Monoxide Dehydrogenase (CODH) were investigated. It shows the pH optimum at 6.3 where the feasibility of electrochemical reduction and the stability of CODH compromise each other. The optimum temperature for the reduction was at 60 degrees C where the enzyme shows the optimum activity although the solubility of carbon dioxide decreases as increasing temperature.