The control of arsenic is important in oxidation roasting and leaching of cobaltite. Oxidation roasting below 823 K did not show any crystal structural change in cobaltite, but heating to 923 K yielded Co-As-oxide, whose composition is varied. Direct oxidation of cobaltite to cobalt oxides with traces of arsenic was observed by roasting at 1023 K or above. The distribution of arsenic within the particles gradually decreased from the outer region to the center of the particles. The arsenic concentration within the particles decreased with the increase of temperature, suggesting temperature dependence on arsenic removal from the lattice of cobaltite. In this article, the process mineralogy of the oxidation of cobaltite is presented at various temperatures. The results from X-ray diffraction (XRD) analysis, reflected light microscopic analysis, and scanning electron microscopic analysis of the roasted cobaltite concentrates together with a rationalized thermodynamic analysis are presented.