Catalytic decomposition of toluene (C 6 H 5 CH 3 ) or benzene (C 6 H 6 ) with inexpensive limonite ores, composed mainly of goethite (α-FeOOH), was examined using a vertical, cylindrical flow fixed-bed quartz reactor to develop a novel method of removing biomass-derived tar components. The unsupported limonite catalyst was active for the decomposition of 480 ppm of C 6 H 5 CH 3 and 1700 ppm of C 6 H 6 in 15 vol % H 2 O/45 vol % H 2 /He, leading to C 6 H 5 CH 3 and C 6 H 6 conversions at 500 °C of nearly 100 and 97%, respectively. When the C 6 H 5 CH 3 decomposition temperature was increased from 500 to 800 °C, the overall reaction path changed from demethylation to hydrocracking and then to steam reforming. A honeycomb-supported limonite catalyst also was effective and achieved nearly complete C 6 H 5 CH 3 conversion at 600 °C. In addition, the honeycombsupported catalyst promoted C 6 H 6 conversion of nearly 100% without carbon deposits at 700 °C in 15 vol % H 2 O/20 vol % H 2 / 26 vol % CO/20 vol % CO 2 /5 vol % CH 4 that was designed to simulate raw fuel gas derived from biomass gasification. Powder X-ray diffraction (XRD) measurements after reaction at 700−800 °C revealed the presence of finely dispersed metallic iron (α-Fe), which is likely responsible for the high catalytic performance.