In this work, the thermal activation of different catalytic systems based on Ni (bulk and supported) was analyzed. These solids are used to obtain synthesis gas from reforming of methane. The evolution of these systems during calcination in air atmosphere was studied by using differential thermal analysis, thermogravimetry analysis and X-ray diffraction. Results obtained, allowed the determination of calcination temperatures necessary for decomposition of precursors of active phases (for different prep aration methods) as well as definition of a route to obtain supported Ni catalysts via deposition-precipitation with urea.