Pyrites can be oxidized by the bacterium A cidithiobacillus ferrooxidans (At. f), producing H2SO4 and FeSO4. Rock phosphate is dissolved by H2SO4, forming soluble phosphorus. Fe2+ in FeSO4 is oxidized to Fe3+, producing energy to sustain the growth of At. f The effects of four factors (rock phosphate dosage, pyrite dosage, culture temperature and time) on the fraction of phosphorous leached were investigated. It is suggested that the optimal conditions are as follows: rock phosphate dosage 1 g/L, pyrite dosage 30 g/L, culture temperature 30 degrees C, culture time 84 h. The fraction of phosphorous leached is up to 11.8%. (C) 2005 Elsevier Ltd. All rights reserved.