Large quantities of catalysts are used in the Egyptian refining industry for the purification and upgrading of various petroleum streams. These catalysts gradually lose activity through deactivation with time, and the spent catalysts are usually discarded as solid wastes. Studies were conducted on rejuvenation, reclamation of metals, and reuse of the spent hydrotreating catalyst, Mo-Ni/Al2O3, which has been used in re-refining of waste lube oil derived from the Alexandria Petroleum Company. Its lifetime after several regeneration operations was five years. Selective leaching treatments were carried out with organic oxalic acid in order to rejuvenate the spent catalyst for use in other reactions or metal recovery. The results indicated that 4% oxalic acid oxidized by 5% H2O2 was the most efficient leaching solvent to facilitate the metal removal and the rejuvenated catalyst characterized by the unchanged crystalline phase of the catalyst. Four percent oxalic acid leaching solution gave total active and non-active metal removal 17.4% and 45.6% for coked and decoked catalyst samples, while the selective removal for the active Mo and Ni metals was 69.87% and 24.63%, respectively. The activity of the rejuvenated catalyst was tested for hydrodesulfurization (HDS) of vacuum gas oil under reactor temperature 300 degrees C-380 degrees C and hydrogenation of heptene-2 under different GLC-pulse reactor temperature 200 degrees C-400 degrees C. The results indicated that the rejuvenation technique introduced a catalyst having an HDS-activity that nearly approached that of the fresh catalyst sample of the same type, i.e., 94% and 98%, respectively, and other types that have hydrogenation activity can be used in petrochemical hydroprocessing at lower temperatures. The selective recovery of Mo, Ni, and Al from the spent catalyst was processed well by the aid of acid leaching and gave metal recovery as metal salts. Therefore, this work can provide a complete solution to the environmental problem of spent hydroprocessing catalysts in a profitable way.