By employing a rotating cylinder system, the roles of mechanical abrasion and electrochemical dissolution during Al CMP were studied. Under rotating and abrasive conditions, both the total metal removal rate and the electrochemical dissolution rate of Al in 5 vol.% phosphoric acid + 0.5 M citric acid solution (pH 4) increased with an increase in both contact pressure and specimen rotation speed. However, the contribution of electrochemical dissolution to the total removal rate of Al was less than that of mechanical abrasion with a contact force in the range of 0.98-4.90 N. After the abrasive test, metallic Al was present in the solution, indicating that passive him was not the sole material removed under the chemical-mechanical abrasion condition.