The hydroprocessing activities of Maya heavy crude oil were investigated on NiW catalysts. Two types of supports, carbon modified ultra-stable Y zeolite (AZ) and Y zeolite-carbon (AZC), were prepared. SEM and TEM results show that tungsten phases are well dispersed on carbon modified support whereas these phases are preferentially distributed on part of the carbon covered zeolite support. It is also observed that more stacking of WS(2) slabs are present in zeolite-carbon support and it is due to weak interaction of metal with carbon covered support. HDM and HDS activities increase with increasing percentage of carbon on support and the support having 10 wt% of carbon shows the highest activities. It is also observed that AZ supported catalysts have higher hydrotreating activities compared with the AZC supported NiW catalysts. Deactivation studies show that the presence of carbon into the support may delay deactivation rate during hydrotreating of heavy oil. (C) 2009 Elsevier B.V. All rights reserved.