Commercial liquid-phase-sulfided type II CoMo/Al2O3 catalyst was reactivated after commercial operation and oxidative regeneration. For this purpose, the use of citric acid (CA) that reactivates a regenerated CoMo/Al2O3 catalyst was studied. The study of the reactivated catalyst was carried out by means of UV-DRS, FTIR, Raman spectroscopy, XRD, XPS, and HTREM. The catalytic activity was estimated in the HDS of straight-run gasoil (SRGO). It was shown that the treatment of the catalyst with CA leads to the formation of a Co-Mo complex compound and significantly reduces the proportion of beta-CoMoO4 and MoO3 in the catalyst. Eventually, this leads to the formation of CoMoS phase type II in a higher proportion enhancing the HDS catalytic properties. [GRAPHICS] .