Dissolution behaviour of metals in Ni-Mo hydrodesulphurization catalyst waste was investigated in a 1 L jacketed glass reactor. Samples were roasted at 500 degrees C in a tube furnace for the removal of C and S prior to the dissolution experiments. It was determined that roasted samples consisted of mainly 27.692% Al, 20.238% Mo, 5.267% Ni and 4.331% P. Unmilled samples were used for dissolution experiments because dissolution experiments carried out with milled and unmilled samples showed that milling has no significant effect on the dissolution rate. Oxalic acid solutions with 0.25-1 M, reaction temperatures of 25-70 degrees C and solid to liquid ratios of 10-100 g L-1 were used as experimental parameters. It was found that the dissolution behaviour of Ni is different from Al, Mo and P. 92% of Mo, 19% of Ni, 28% of Al and 72% of P were dissolved at optimum dissolution conditions.