The kinetics of molybdenum, nickel, vanadium and aluminium leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide was investigated. The effects of temperature and particle size were examined. In addition, the reaction mechanism for the dissolution of the spent catalyst was discussed. The results of the kinetic analysis for various experimental conditions indicated that the reaction rate of leaching process is controlled by chemical reaction at the particle surface. The values of the activation energies of 31 +/- 2,36 +/- 4.30 +/- 4 and 57 +/- 3 kJ mol(-1) for Mo, Ni, v and Al, respectively, are characteristic for mechanism controlled by chemical reaction. (C) 2010 Elsevier B.V. All rights reserved.