Ni/perovskite-type oxide catalyst (Ni/La0.7Sr0.3AlO2.85: LSAO) shows high catalytic activity and low carbon formation during the steam reforming of aromatic hydrocarbons because of the high mobility of lattice oxygen in the support. The reaction mechanisms of the catalyst were investigated by characterizations and catalytic activity tests for steam reforming of various hydrocarbons including toluene, methylcyclohexane, and n-heptane. The catalytic performance was affected by the reactant structure, as revealed by Arrhenius plots and FT-IR analyses. Adsorption state and stability of reaction intermediates were very important factors in the catalytic activity for steam reforming.