Periodic density functional theory (DFT) calculations were performed to investigate the hydrodenitrogenation (HDN) mechanism of pyridine on MoP(0 1 0). The geometries and energies for the adsorbed pyridine were first described, and then the competition between hydrogenation and denitrification of pyridine were analysed to elaborate the HDN mechanism. Our results show that pyridine has side-on and end-on adsorption modes on MoP(0 1 0), in which the most stable η4(N1,C2,C3,C5) configuration of the side-on mode facilitates the hydrogenation of pyridine. The favourable HDN pathway of pyridine proceeds along the pyridine → 4-Monohypyridine → 3,4-Dihydropyridine → 1,3,4-Trihydropyridine → 1,3,4,5-Tetrahydropyridine → CH(CH2)3CHNH route. The denitrification process could not exhibit the competitive advantage until after the fourth hydrogenation step of 1,3,4,5-Tetrahydropyridine. This theoretical work provides further information on the HDN mechanism of pyridine on MoP(0 1 0), and also provides insight into the understanding of competition between hydrogenation and denitrification.