Individual and simultaneous hydrodenitrogenations (HDN) of aniline and pyridine were examined over Ni-Mo-P/alumina catalyst. The HDN rate of aniline was greater than that of pyridine when each HDN reaction was carried out separately. HDN of aniline, however, was inhibited by pyridine when the HDN of aniline and pyridine mixture was examined. Both individual and simultaneous reactions of aniline and pyridine were quantitatively predicted by Langmuir-Hinshelwood equations. Adsorption strengths and HDN rate constants of aniline and pyridine in the equations were kinetically estimated from experimental results.