Three different Mn-promoted Ni/γ-Al2O3 catalysts, Mn/Ni/γ-Al2O3, Mn-Ni/γ-Al2O3 and Ni/Mn/γ-Al2O3, were prepared and applied to the steam reforming of liquid petroleum gas (LPG) mainly composed of propane and butane. For comparison, Ni/γ-Al2O3 catalysts containing different amount of Ni were also examined. In the case of the Ni/γ-Al2O3 catalysts, 4.1 wt% Ni/γ-Al2O3 showed the stable catalytic activity with the least amount of coke formation. Among the various Mn-promoted Ni/γ-Al2O3 catalysts, Mn/Ni/γ-Al2O3 showed the stable catalytic activity with the least amount of coke formation. It also exhibited a similar H2 formation rate compared with Ni/γ-Al2O3. Several characterization techniques--N2 adsorption/desorption, X-ray diffraction (XRD), CO chemisorptions, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and CHNS analysis--were employed to characterize the catalysts. The catalytic activity increased with increasing amount of chemisorbed CO for the Mn-promoted Ni/γ-Al2O3 catalysts. The highest proportion of Mn^(4+) species was observed for the most stable catalyst.