Abstract: βMo2N0.78 as a hydrodesulfurization(HDS) catalyst shows high activity in HDS reaction of sulfurous model compounds, which was reported in previous works. Therefore, the changes of the catalyst composition and structure after HDS reaction and the influences of aftertreatment on HDS catalytic activity were studied in this paper. The XRD results indicate that the bulk structure of βMo2N0.78catalyst is kept unchanged, though the catalyst surface is sulfided and the oxynitride is consumed at HDS condition. And the hydrogen reduction treatment of βMo2N0.78 catalyst before and after HDS reaction can not improve the catalytic activity. Presulfided βMo2N0.78 has a similar HDS activity with that of passivated sample at its stable stage. Second passivation of the catalyst after HDS reaction can recovery the catalytic activity.