This study compared the abilities of various materials to catalyse the decomposition of tar constituents in fuel gas. The materials were tested on a sample gas flow from an industrial-scale peat-fired updraft gasification process. The tar content of the gas was about 100 g m−3. When the treatment temperature was 900 °C, and the gas residence time in the catalyst bed was 0.3 s, the ability of the tested materials to decompose tar decreased in the order: commercial nickel catalyst (Ni on Al2O3) >dolomite >activatedaluminacatalyst >silica-aluminacatalyst >siliconcarbide (inert). With the nickel catalyst the tar and light hydrocarbons contained in the gas were almost completely decomposed into gases (CO, H2). An increase in the water content of the gasifier fuel resulted in a reduction in the tar content and an increase in the ratio of the treated gas. The most important effect of the catalyst appeared to be the catalysis of the reactions between the intermediate thermal degradation products, such as light hydrocarbons and deposited carbon, and water vapour.