The main objective of this work is to study the support effect on hydroprocessing of Maya heavy crude. In this respect, we have used three different supports-alumina, alumina-silica, and alumina-titania. CoMo catalysts are prepared by using these three supports. The catalysts are characterized by XRD, TPR, and pore size distribution. Alumina, that is prepared by the pH swing method has pore structure in a wide range. TPR profiles are support sensitive (i.e., the reduction behaviors are different for differently supported catalyst). A low-temperature sharp peak is observed in an alumina-silica supported catalyst, whereas more than one reduction peak is found on alumina and alumina-titania supported catalysts. The complex reduction profiles of the alumina-titania supported catalyst indicate the presence of several superimposed molybdenum phases. The activity results expressed as time weighted mean conversions show that there is indeed a support effect on the hydroprocessing of Maya heavy crude. Catalysts supported by alumina-titania show comparatively high mean activities and stability with respect to time-on-stream. It may be due to the presence of more. reducible molybdenum phases and favorable pore structure. The deactivation rate is faster for the catalyst which has high coke or metal deposition tendency.