The dissolution kinetics of natural pyrite samples in Cl-2-saturated carbon tetrachloride and water-carbon tetrachloride media have been investigated, The effects of pyrite particle size, reaction time, temperature, stirring speed and water-to-carbon tetrachloride ratio were studied. The dissolution rate of pyrite in these media increased with increase in temperature and decrease in particle size, In water-carbon tetrachloride medium, the rate was independent of the stirring speed, However, in carbon tetrachloride medium alone, the increase in the stirring speed significantly increased the dissolution rate, The experimental data were analyzed on the basis of unreacted shrinking core model, It has been found that the dissolution is controlled by diffusion through the ash layer in carbon tetrachloride and that it is chemically-controlled in water-carbon tetrachloride medium. The activation energies for the diffusion- and the chemically-controled steps were 32.3 and 22.3 kJ mol(-1), respectively.