Mathematical model describing the balances and kinetics of the denitrification process has been formulated. The model includes the balance of carbon, nitrogen and electrons, which are transferred onto nitrates in the oxygen free respiration. Both carbon and nitrogen limitations are taken into account in the kinetics equation. Two denitrifying bacterial strains, Ervinia sp. and Alcaligenes denitrificans, were used in the experimental studies. Bacterial cultures were carried out in a continuous reactor. The maximum efficiency of the nitrogen removal for the optimum dilution rate has been found. The model parameters have been estimated.