Using K led to the simultaneous decrease of Ni(Co)WS and rise of Ni(Co)Sx. K adding poisoned the active sites and declined selectivity of Ni(Co)PW/Al2O3. Modified catalysts can be ranged on the activity KWS < KNiWS << CoSx+KWS. Increase of HDS/HYDO selectivity is followed by a decrease of HDS conversion. The relevance of modifying catalyst with K strongly depends on a S content in feed.