A catalyst of 10% Ni/gamma -Al2O3 for CO2/CH4 reforming was prepared and characterized by TPR. TPD. XPS, XRD and activity measurements. XPS and TPR showed that Ni mainly exists in the form of NiAl2O4 in the calcined catalyst and is hard to reduce below 650 degreesC, indicating a strong interaction between metal and support. Reduction of the calcined catalyst results in fine particles of Ni-0. with an average diameter of about 20 nm as determined by XRD. The uptake of H on the reduced catalyst measured by H-2-TPD is 4.2-4.6 mole per mole of Ni species and does not depend on the reduction degree of Ni species. This provides a convincing piece of evidence for the occurrence of hydrogen spillover in the reduced catalyst. Only reduced catalysts present good activity, but the degree of nickel reduction has almost no effect on the reforming activity. This seems to suggest that Ni-0 is vital for the reforming activity, but gamma -Al2O3 is also involved in CO2/CH4 reforming and contributes even more. Based on the mechanism proposed by Bradford et al. and on our observations, a mechanistic model has been proposed to elucidate the role of gamma -Al2O3 in CO2/CH4 reforming.