Two supports, one prepared in our laboratory and other supplied commercially, were used to prepare CoMo and NiMo catalysts. A commercial catalyst was also used as a reference in our present investigation. These catalysts were characterized by XRD and TPR experiments. HDM, HDS, HDN and HDAsp reactions were carried out in a microreactor using a mixture of Maya crude with naphtha as feed. The deactivation of catalysts was also studied. XRD results revealed that the active metals were well dispersed into the supports. Two broad peaks were observed on promoted catalysts in our TPR experiment. Lower temperature peak was assigned as reduction of multilayer MoO3 species and higher temperature peak was due to reduction of monolayer MoO3 species. The reduction peak patterns were different for respective catalysts. The catalyst deactivation was observed with time on the stream and it was faster at initial period of reaction. The coke formation was prime concerned for the deactivation of these catalysts as well as the decrease of specific surface area. The activities were correlated with the pore structure of the catalyst. (C) 2004 Elsevier B.V. All rights reserved.