The hydroprocessing of fuels containing relatively large amounts of organonitrogen compounds becomes increasingly important in the upgrading of hydrocarbon fuels. Therefore, to investigate the removal of organonitrogen compounds, the hydrodenitrogenation of pyridine dissolved in n-heptane was studied over sulfided Ni-Mo/u-Al₂O₃ catalysts in the range of temperature between 513K and 633K and pressure between 30bar and 50bar in a fixed bed flow reactor. Pyridine conversion increased with the increased temperature and pressure, and the piperidine formation was found to be irreversible. Pyridine concentration reached a maximum at about 573K and the apparent reaction order was found to be one with respect to pyridine.