Conventional HDS-catalysts consist of Co and Mo supported on Y-Al2O3. The addition of Zn as a second promoter or the alumina acidification with F increase the catalitye activity in HDS of commercial feeds (Fierro et al., 1984; Boorman et al., 1984). In this paper the combined effect of both Zn and F incorporation is discussed. A series of Zn-Co-Mo catalysts supported on fluorinated alumina (0.0 –2.0 wt% F) was prepared and tested for HDS activity using a commercial gas-oil. The data gathered showed a decrease in HDS activity for intermediate F contents (0.4 – 1.0 wt%). This result could be tentatively explained through alumina surface deterioration during impregnation with NH4HF2solutions al low pH.