In this study, a transient biofilter model for binary volatile organic compound (VOC) mixture is developed. In the model, general mixing, oxygen limitation aspects, multicomponent adsorption phenomena, Monod- and Andrews-type kinetics with interference between the components are considered. Multicomponent adsorption isotherms are developed and used in the solution of the model. The model has been solved by two approaches, (approximate and general) and validated with biofiltration of benzene-toluene mixture data of previous work. The approximate model is based on the quasi-steady-state approximation in the biofilm, but the general model is solved as it is without any simplifications. The results show that the predictions by the general model are closer to the actual experimental results. It was also found that inlet oxygen composition plays an important role in the biofiltration of mixed VOC removal, specially at high inlet concentrations.