The dynamic changes in activity and selectivity for the CO2 reforming of CH4 over unsupported and supported Ni catalysts were investigated. The reduced NiO has low initial conversions of CH4 and CO2, which decrease rapidly with time. The mixture of powders of NiO and Al2O3 has low initial conversions of CH4 and CO2 and a low yield to CO, which, however, increase with reaction time, due most likely to Ni migration to Al2O3. In contrast, the reduced 1 wt% Ni/Al2O3 catalyst (reduced from NiO/Al2O3) has high initial conversions and CO yield, which slowly decrease with time due to carbon deposition. The reduced 13.6 wt% Ni/Al2O3 catalyst has high initial conversions and CO yield, but, because of carbon deposition, the reactor was completely plugged in 6 h. The reduced 1 wt% Ni/SiO2 catalyst has moderate initial activity and CO yield, which decay fast with reaction time. The reduced 13.6 wt% Ni/SiO2 has a high initial activity and CO yield, which decay slowly with reaction time. The reduced 13.6 wt% Ni/TiO2 has a moderate initial activity and CO yield, which decay with reaction time. Carbon deposition was found to occur over all these catalysts, and the sequence of carbon deposition was : 13.6 wt% Ni/Al2O3 > 13.6 wt% Ni/SiO2 > the reduced mixture of NiO and Al2O3(13.6 wt% Ni) > 13.6 wt% Ni/TiO2 > 1 wt% Ni/Al2O3 > 1 wt% Ni/SiO2.