The degradation of phenol under microelectrolysis was enhanced by O-2-microbubbles. Phenol solution was circled in a microbubble-assisted microelectrolysis reactor under acid conditions. The degradation rate of phenol reached 65% within 2 h with O-2-microbubbles, compared to 9.5% and 4% with air-and N-2-microbubbles due to better dissolution of oxygen with finer microbubbles and at higher dissolution pressure. Higher efficiencies of phenol degradation at lower temperature further confirm the role of dissolved oxygen. In the microbubble-assisted microelectrolysis system dissolved oxygen, carbon steel pellets, and sulfuric acid are necessary conditions for the oxidation of phenol. The conversion of phenol increases with an increasing amount of carbon steel pellets and/or sulfuric acid. Catechol, hydroquinone, and low-molecular-weight carboxylic acids are the major products.