This study investigated the effects of various factors on the oxidation reactions of arsenic trioxide in the nitric acid solution. The oxidation rate of As₂O₃was increased with the addition of hydrochloric acid as a catalyst and was not affected by stirring of the solution. The most favorable concentration of HNO₃for oxidation of As₂O₃was found to be 12N, and no oxidation reaction occurred below 4N. The acidity of this reaction involves both homogeneous and heterogenous reactions, and the initial reaction rate was obtained as a following empirical equation at 7N HNO₃, 0.4g/L HCI and 75℃. (수식)