In this study, the catalytic combustion of propionaldehyde, which is an Offensive Odorant Substance assigned by the Korean Ministry of Environment (KMOE), over alumina-supported manganese oxide (Mn/Al2O3) catalysts was investigated. The combustion reaction was carried out in a fixed-bed reactor at the temperature range of 200~340 ℃. Mn/Al2O3 catalysts with Mn loadings ranging from 3.9 to 18.3 wt.% were prepared by impregnation method. The physicochemical characteristics of the catalysts were analyzed by X-Ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Brunauer-Emmett-Teller (BET). The Mn crystalline phases of the Mn/Al2O3 catalysts were identified as α-Mn2O3 and β-MnO2. Mn oxides were covered on γ-Al2O3 supports with an average diameter of around 10 μm. With the increase of Mn loadings, the BET surface areas, pore volumes and average pore diameters of the Mn/Al2O3 catalysts decreased. The catalytic activities of Mn/Al2O3 catalysts increased as the Mn loading was increased from 3.9 wt.% to 18.3 wt.%. The catalyst with 18.3 wt.% Mn loading was able to achieve 100% propionaldehyde conversion at 260 ℃. For the same temperature, a lower Gas Hourly Space Velocity (GHSV) and a lower propionaldehyde concentration promote the complete combustion of propionaldehyde.