The catalytic combustion of acetaldehyde was studied using various types of Co oxides and Co-PC. The Co oxides and Co-PC were characterized using an X-ray diffractometer (XRD), X-ray photo-electron spectroscopy (XPS), and a particle sizing analyzer. The Co-PC and CoO were converted into Co₃O₄ under an air atmosphere at 450 °C, and the results were confirmed using the XRD and XPS. According to the pretreatment of the Co-PC and Co oxides, the conversion of acetaldehyde increased. The order of particle size for both fresh and pretreated samples is summarized as follows: CoO < Co-PC < Co3O4 powder < Co₃O₄ (99.995%). For all samples, acetaldehyde was not observed at temperatures above 320 °C owing to complete combustion. The conversion of acetaldehyde in the samples was affected by the fresh state of the Co oxides and the space velocity. The catalytic activity depended on the chemical state of the Co oxides and the surface concentrations of Co, O, and N.