The crossover rate of ethanol or methanol through membrane electrode assembly (MEA) and MEA components was studied quantitatively at 25 and 60 • C by cyclic voltammetry method. The results obtained in this work show that cyclic voltammetry is a powerful technique to assess the crossover phenomenon through MEA components and structures. In all cases, the ethanol crossover rates are lower than those of methanol. The ethanol and methanol crossover rates depend upon time and temperature. For an initial concentration of 1 M of ethanol or methanol, the crossover rate increases to a maximum after the first hour of the cell operation and then decreases gradually to a certain concentration after the third hour. At 60 • C, the maximum concentration of ethanol crossover rate is lower than that obtained at 25 • C. The crossover rate of ethanol or methanol through MEA is lower than through the components alone (pressed or nonpressed membranes or gas diffusion electrode). 