This paper presents an experimental study of the impact of toluene on the performance of anode-supported (AS) Ni/YSZ SOFC operating at ∼800 °C, 0.25 A/cm2 fed with H2 and biosyngas. Toluene was added to the fuel stream and its concentration increased from tens to thousands of ppmv. Each poisoning test was followed by a recovery step. The main goal of this work is to define a concentration threshold of toluene as a model tar compound and to identify the degradation mechanism caused by this tar compound. Polarization behavior, IV and electrochemical impedance spectroscopy (EIS) were analyzed to evaluate the cell performance. A linear degradation is observed at concentrations above 1000 ppmv for the cell which was fed with H2. The degradation was due to local C(s) deposition. By contrast, toluene even up to 3500 ppm did not cause an increased degradation when the cell was fed with reformed biosyngas. © The Electrochemical Society.