The changes in surface properties and the leaching of chalcopyrite CuFeS 2 after ultrafine grinding are examined. Surface area measurement and photoelectron spectroscopy (XPS) were used for characterization of the ground samples. A gradual decrease in the particle size, from 32 μm, for as received CuFeS 2 , to 2 μm, for the sample ground for 60 min, as well as increasing the surface area from O.23 m 2 g - 1 to 2.68 m 2 g - 1 for equal samples was observed. Analysis of the XPS line of sulphur S2p electrons has shown the existence of sulphur in three different chemical forms: S 2 - , S 0 and S 6 + . The ground samples exhibited a greater proportion of higher oxidation states. The samples were chemically preleached with an acid solution of Fe(III) sulphate to an equal conversion degree (ε C u = 25%), characterized and subsequently leached by the bacteriaThiobacillus thiooxidans . While the rate of chemical leaching is proportional to the increase in CuFeS 2 surface area, the rate of subsequent bacterial leaching is limited by 15 min grinding. The different behaviour of the samples ground for a long time may be explained by differences in the chemical composition of surface layers.