In this work maximum concentrations of the impurities hydrogen chloride and hydrogen sulfide in synthetic wood gas for operation of a Solid Oxide Fuel Cell (SOFC) at different working temperatures and flow conditions are reported. Additionally, an analysis of the influence of the impurity concentrations during the heating up and cooling down phases of the SOFC is given. The paper also deals with wood gas which is generated by a fluidized bed steam gasifier or made by air gasification. It was found that operation with up to 50 ppm hydrogen chloride in hydrogen was possible. Also stable cell performances could be observed with the combination of 10 ppm hydrogen chloride and 3 ppm hydrogen sulfide in the fuel. Wood gas from air gasification always lead to a stable performance but wood gas from steam gasifier sometimes caused power degradation.