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The precoating effect of La2O3 on the performance of Ni/-Al2O3 catalyst for carbon dioxide reforming of CH4 was investigated. All the catalysts showed a fairly good stability while the addition of La2O3 significantly improved the activity of Ni/-Al2O3. Ni/La2O3/Al2O3 catalysts had an optimum amount of La2O3 loading with a La/Al ratio of 0.05 with the highest activity and stability. The catalysts were characterized by BET, XRD, XPS and TPR techniques. The phase of the precoated La2O3 was changed from highly dispersed La species to well crystallized LaAlO3 with increasing La/Al ratio. The interaction between Ni and the support was changed with the addition of La2O3 and the variation of La/Al ratio. Based on the characterization results, the promotional effect of La2O3 on Ni/-Al2O3 resulted from (1) the chemical environment and electronic state of Ni in Ni-La interface, (2) the stabilization of La2O3 on Al2O3 and (3) the strong basicity of La2O3. It was suggested that the highly dispersed La species is more effective than LaAlO3 for the promotional effect of La2O3.