This paper presents a systematical evaluation of the effects of CO2, H2O, CO, N-2 and CH4 in the coal syngas on the properties of typical Ni/YSZ anode-supported solid oxide fuel cells (SOFCs). The results show that CO2, H2O, CO, N-2 and CH4 have complicated effects on the cell performance and the electrochemical impedance spectra (EIS) analysis reveals the addition of these gases influences electrode processes such as the oxygen ion exchange from YSZ to anode TPBs, the charge transfer at the anode TPBs, gas diffusion and conversion at the anode. Two kinds of mixture gases with different compositions are thus constituted and used as fuel for aging test on two cells at 750 degrees C. No degradation or carbon deposition is observed for the cell fueled with 40% H-2-20% CO-20% H2O-20% CO2 for 360h while the cell fueled with 50% H-2-30% CO-10% H2O-10% CO2 exhibits an abrupt degradation after 50 h due to the severe carbon deposition. (C) 2009 Elsevier B.V. All rights reserved.