Abstract: Dissociative adsorption and electrooxidation of dimethyl ether (DME) on a platinumelectrode in different pH solutions were studied using cyclic voltammetry (CV) and in situ FTIR reflection spectroscopy. The coverage of the dissociative adsorbed species was measured about 70% from hydrogen adsorption-desorption region (0.05-0.35 V(vs RHE)) of steady-state voltammogram recorded in 0.1 mol·L-1 H2SO4 solution. It was found that the electrochemical reactivity of DME was pH dependent, i.e., the larger the pH value was, the less the reactivity of DME would be. No perceptible reactivity of DME in 0.1 mol·L-1NaOHsolution could be detected. It was revealed that the protonation of the oxygen atom in the C—O—C bond played a key role in the electrooxidation of DME. In situ FTIR spectroscopic results illustrated that linearly bonded CO (COL) species determined at low potential region were derived from the dissociative adsorption of DME and behaved as‘poisoning’intermediate. The COL species could be oxidized to CO2 at potential higher than 0.55 V (vs RHE), and in the potential range from 0.75 to 1.00 V (vs RHE) DME was oxidized simultaneously via HCOOH species that were identified as the reactive intermediates.