A spent hydrodesulphurization (HDS) catalyst Ni,Mo/Al₂O₃ has been studied by means of X-ray diffraction, scanning electron microscope, electron microprobe and chemical analysis. Chemical analysis of catalyst confirmed its partial chemical composition as follows: Ni (5.26%), Mo (5.08%), Al (24.57%), V (5.36%), S (9.64%), C (17.63%), H (1.14%). Powder XRD analysis showed that the main phase of studied catalyst is γ-Al₂O₃ while V₅S₈ and Ni₃S₄ were also detected. SEM results confirmed that V and Ni sulphides are deposited on the surface. The surface area of the catalyst determined by nitrogen adsorption (BET method) was found equal to 80.1 m²/g. Leaching tests of the spent catalyst in solutions of sulphuric acid as well as oxalic acid with oxidizing agents such as NH₄NO₃, (NH₄)₂S₂O₈ and H₂O₂ have been carried out.