The catalytic oxidation of a model biomass tar, toluene, was studied using platinum and ruthenium on γ-alumina catalysts at various temperature, catalyst sizes, and metal contents in an environment with either the presence or absence of syngas. As the reaction temperature increased and the size of the catalyst decreased, the conversion of toluene increased. Usually, the higher content of platinum and ruthenium in the catalyst showed higher conversion of toluene. It was found that the presence or absence of syngas greatly affected the toluene conversion. The platinum catalyst showed a higher toluene conversion efficiency than the ruthenium catalyst at the same temperature in the absence of syngas, while in the presence of syngas, the ruthenium catalyst showed a better conversion efficiency than the platinum catalyst. The results indicate that a temperature of over 300 °C is required in order to oxidize tar efficiently using these catalysts.