According to the high operating temperature of Solid Oxide Fuel Cell (SOFC) (700-1100ºC), it is known that some hydrocarbon fuels can be directly used as inlet fuel instead of hydrogen by feeding straight to the anode. This operation is called a direct internal reforming SOFC (DIR-SOFC). However, the major difficulty of this operation is the possible degradation of anode by the carbon deposition, as the carbon species are easily formed. In the present work, the effect of inlet fuel (i.e. H2, synthesis gas (H2+CO), CH4, CH4+H2O, CH3OH+H2O, and C2H5OH+H2O) on the degradation of nickel cermet (Ni/YSZ), which is the most common anode material of SOFC, was studied.It was found from the work that hydrogen and synthesis gas (CO+H2) are proper to be used as direct inlet fuels for DIR-SOFC with Ni/YSZ anode, since the carbon formation on Ni/YSZ occurred in the small quantity. The mixture of methane and steam (CH4+H2O) can also be used as the inlet feed, but the H2O/CH4 ratio plays an important role. In contrast, pure methane (CH4), methanol with steam (CH3OH+H2O) and ethanol with steam (C2H5OH+H2O) are not suitable for using as direct inlet fuel for DIR-SOFC with Ni/YSZ anode even the higher H2O/CH3OH and H2O/C2H5OH ratios were applied.