The present work is focused on the role of an organic promoter (triethyleneglycol - TEG) on the activity of hydrotreating catalysts. By impregnating such compound on oxidic industrial catalyst, an enhancement of the catalytic activity in the HDS conversion of 4,6-DMDBT as well as SRGO HDS was obtained. Using several physico-chemical techniques and in situ characterization (Raman. XAS), it was found that TEG affected the coordination of Co and Mo in the oxidic species. During the activation procedure, the presence of TEG slows down the sulfidation and allows the genesis of more active "CoMoS" species. (C) 2011 Elsevier B.V. All rights reserved.