Plasma techniques are attracting significant attention in the context of tar removal from the biomass-derived syngas. This research investigated the impact of microwave (MW) plasma on a simulated biomass syngas containing benzene as a model tar compound. The high temperature of the plasma and the presence of reactive species resulted in crucial changes of the gas composition. A significant increase in CO and H-2 concentrations at a cost of CH4 and CO2 was observed. It was concluded that CO2 and H-2 were essential in the conversion of both, methane and benzene. This phenomenon was attributed to the presence of O, OH and H radicals generated in the plasma core zone. While the addition of these compounds allowed achieving conversion efficiency at the level of 97-98%, the presence of methane decreased it to c.a. 60% due to the re-formation of benzene. Moreover, the main by-products of benzene conversion, qualified and quantified, showed the same tendency towards syngas compounds as benzene did.