Electrochemical and photoelectrochemical experiments were conducted to investigate the pyrite/aqueous interface reaction by using microparticles of synthetic pyrite as electrodes. The potential of the conduction bandedge of pyrite as a function of pH was estimated to be E(c) = 0.34 - 0.059 pH in volts us. saturated calomel electrode (SCE). The open-circuit potential of pyrite electrode in 1 M HNO3 solution was 0.38 V-SCE. Illumination of pyrite microelectrodes increased the anodic current and the dissolution rate dramatically but had little effect on the cathodic current and the cathodic dissolution. These results indicate that pyrite, as an n-type semiconductor, dissolves anodically through a hole transfer (valence band) pathway, while cathodic dissolution only involves electron reaction (conduction band).