The oxidation of 200/270 mesh and 150/200 mesh stibnite was carried out at the temperature range of 340℃-440℃. The results obtained in this study are as follows; 1) The rate for the oxidation process of 200/270 mesh Sb₂S₃at the temperature between 340℃ and 370℃ is controlled by the chemical reaction at the reaction surface, while, in the region 380℃-440℃, the rate is controlled by the oxygen diffusion through the product layer. 2) The reaction of the oxidation of 150/200 mesh Sb₂S₃is chemically controlled at the temperature range of 340℃-380℃, while in the region 400℃-440℃ the rate is controlled by the diffusion. 3) The effect of oxygen concentration on the oxidation decreases as the temperature increases. 4) The effect of the size on the reaction decreases as increasing the temperature.