A series of molybdenum nitride (Mo₂N) catalysts were prepared by a topotactic synthesis method using a TPR (Temperature Programmed Reaction) at various conditions (temperature ramping rate, NH₃ gas flow rate, final preparation temperature). The surface property and acidity of Mo₂N catalysts prepared at various prepared conditions were studied by SEM, XRD, BET, FT-IR and TGA. The hydrodenitrogenation (HDN) of pyridine in n-heptane over Mo₂N catalyst (A1) was studied in a fixed bed continuous flow reactor (CATATEST) at the temperatures between 250-450℃, the pressure at 20-40X10⁵ Pa and the contact time between 0.01-0.05 g cat.hr./ml feed. The microstructure of Mo₂N catalyst was not changed at various preparation conditions by topotactic reaction. The XRD and BET studies showed that the extent of the crystallinity and the surface area of the prepared Mo₂N catalysts increased when the final preparation temperature in creased and the temperature ramping rate was lowered. In addition, from the TGA curve, the acid strength increased with the increase of the NH₃ gas flow rate. The results of pyridine hydrodenitrogena-tion(HDN) over Mo₂N catalyst showed that the catalytic activity (conversion %) increased as reaction temperature, reaction pressure, and contact time increases. The selectivity for piperidine possessed a maximum at 350℃ regardless of the reaction pressure. Also, the selectivity for cracked products increased as reaction temperature and pressure increased. The activation energy was determined 7.16 kcal/mol by Arrehenius plot.