Catalysts with basic properties have been used in many reactions with the aim of inhibiting coke deposition, but the addition of basic dopants may change both their activity and selectivity. In order to find efficient systems to methane steam reforming, the effect of magnesium on the properties of lanthana-supported nickel was investigated in this work. Catalysts with 15% of nickel and lanthanum to magnesium molar ratios of 5 and 10 were prepared and characterized, besides pure magnesia or lanthana-supported nickel. It was found that magnesium makes the nickel reduction more difficult at high temperatures but favors the reduction of amorphous nickel oxide at low temperature. Magnesium also increases the activity of lanthana-supported nickel catalyst in methane steam reforming reaction and affected the hydrogen and carbon monoxide selectivities, showing that it can be used for tailoring catalysts for several purposes. (C) 2008 Elsevier Ltd. All rights reserved.