Three types of cermets based on NiO-ScSZ (A), Ni0.9Mg0.1O-ScSZ (AMg) and Ni0.9Mg0.095Al0.005O-ScSZ (AMgAl) were applied as SOFC anodes. Humidified H-2 and simulated biogas (CH4:CO2 = 6:4) were directly supplied to the anode side of SOFC single cell. Catalytic activities for the reforming and the electrochemical reactions were tested,in a typical electrochemical measurement setup. When hydrogen (3% H2O) was supplied as a fuel, the three anodes showed almost the same voltage losses (anodic overvoltages) of ca. 40 mV at 400 MA cm(-2) at 1000 C. However, supplying the simulated biogas, AMg and AMgAl showed smaller losses of 25 and 29 mV, respectively, than those in supplying hydrogen, whereas A showed the loss of more than 40 mV. Through this study, it was revealed that when the biogas is selected as a fuel, the electrochemical efficiency of the internal reforming SOFC is enhanced by using AMg or AMgAl as anode materials instead of A. Although the higher performances of AMg and AMgAl mainly result from the stability of small Ni particles against sintering, in addition to this effect, basic (Ni,Mg)O solid solution or MgO existing in the electrocatalysts contributes to further activity enhancement. 2006 Elsevier B.V. All rights reserved.