The painting of vehicles in the automobile industry generates large quantities of gaseous emissions which contain volatile organic compounds (VOC) like xylenes. This polluted air has a high moisture content and a temperature around 15-20 degrees C. It is thus possible to consider its treatment by a biological way. In this paper, laboratory tests are described which led to the choice of packing material to make a biofilter having good removal efficiency. Moreover this technique is known for its simplicity and low energy cost. The maximum treatment capacity was obtained with peat. A mathematical model which makes it possible to specify the different limiting steps of the process was carried out. This considered both physical parameters of the biofilter and properties of the biofilm. By choosing a lower Henry's constant than typical air:water system, we obtain a better simulation of the xylenes concentration according to the biofilter length and applied load.