A glass beads-packed bed dielectric barrier discharge reactor is used for the removal of low concentration toluene (330 ppm) in air. The influence of relative humidity (RH) of the air on the discharge characteristics, toluene removal efficiency, and byproduct formation is examined. Optical emission spectroscopy has shown that the amount of N-2 excited states decreases with increasing RH because of the increased quenching of these excited states. A toluene removal efficiency of 42 +/- 2% was obtained at an optimum RH of 40% at a specific input energy of approximately 250 J/L. The main products of the toluene decomposition process were identified as CO2, CO, N2O, O-3 (both dry and humid air) and HCOOH (dry air only). While higher RH suppresses the formation of formic acid, the highest CO and CO2 yields, N2O, and O-3 concentrations at an RH of 40% confirm the observed highest removal efficiency at this experimental condition.