In this study, we characterized steam reforming reactions and surface of Ni/Al2O3 catalysts. Ni-Mo based catalysts were prepared by loading Mo as the co-catalyst and reaction activities of the Ni-Mo based catalysts were compared with those of Ni-based catalysts. Through the H2-TPR and XPS analysis it was confirmed that this characteristic efficiency. O2-TPO analysis was performed to examine the deposition characteristics, bonding structures and evaporation characteristics of carbon deposited on the surface of catalysts after long run experiments were performed for steam reforming reactions. As the results, it was found that durability was improved in Ni-Mo based catalysts inhibiting formation of graphitic carbon species which reduced reaction activities of the catalysts by strongly interacting with Ni in the steam reforming reaction.