In the present work, studies were carried out with the objective of utilizing spent residue hydroprocessing catalysts, which contained coke and metal (V and Ni) deposits, in the preparation of active new catalysts that can be used for hydrodemetallization of residual oils. Three types of spent catalysts that contained different levels of vanadium, molybdenum, and nickel were used in the experiments. These catalysts were collected from different reactors (front, middle, and back-end) of an industrial atmospheric residue desulfurization unit. A series of catalysts were prepared by mixing and kneading of spent catalysts with boehmite in different proportions followed by extrusion of the resulting paste. All prepared catalysts were characterized by chemical analysis and by surface area, pore volume, and pore size measurements, and their hydrodesulfurization (HDS) and hydrodemetallization (HDM) activities were evaluated by hydrotreating tests in a fixed-bed reactor using Kuwait atmospheric residue as feed. A commercial HDM catalyst was also tested under the same operating conditions and its HDM and HDS activities were compared with that of the prepared catalysts. The results revealed that the catalysts prepared from spent catalyst/boehmite blends contained vanadium, molybdenum, and nickel. The relative concentrations of these metals (V, Mo and Ni) in the prepared catalysts and other key properties such as surface area, porosity, and crushing strength showed a strong dependence on the amount and the type of spent catalyst used in the preparation. Forty to 60 wt % of spent catalysts could be mixed with boehmite and extruded to produce active HDM catalysts. Catalysts prepared from the spent catalysts with low vanadium content such as those discarded from the back-end reactors of an atmospheric residue desulfurization unit were more active than a reference commercial HDM catalyst for promoting HDM and HDS reactions. The presence of some kind of new active sites involving a combination of the three metals Mo, Ni, and V together with the reasonably high surface area and porosity could be responsible for the high hydrotreating activity of the catalyst prepared by mixing spent catalyst with boehmite.