The aim of this research is to develop a representative model which simulates the performance of a biofilter used to treat drinking water. A steady-sate model is applied. The Monod-type substrate utilization is used, and the external and the internal mass transfer are neglected in this model. The model describes the process of substrate biodegradation, bacterial attachment onto filter media, and detachment of suspended bacteria. It simulates the natural organic matter (NOM) and biomass profdes in a biofilter as a function of filter depth and filtration velocity. The key biokinetic parameters k and KS are estimated through a special experiment. The results of the model testing show that the model prediction agrees well with the experimental data.