In the present work, the dissolution of copper (II) oxide in ammonium chloride solutions was studied. In the experiments, the following variables were chosen: the solution concentration, reaction temperature, solid-to-liquid ratio, and stirring speed. It was observed that the decrease in the solid-to-liquid ratio, and the increase of the reaction temperature and solution concentration increased the dissolution rate. It was found that the stirring speed had no significant effect on the dissolution rate. The reaction kinetics of copper(II) oxide according to the heterogeneous and homogeneous reaction models were examined and it was found that the dissolution rate was controlled by diffusion from the product layer formed around the particle. The dissolution kinetics can be expressed: 1-3(1-x)(2/3) + 2(1-X) = [5.39 . 10(6)(C)(2.41)(S/L)(-1.14)e(-9785/T)]. t The calculated activation energy was 81.3 kj mol(-1).