A systematic study has been made to establish the reaction mechanism of bioleaching of manganese ore with the manganese reducing fungi, Penicillium citrinum, isolated from the top soil of an active manganese ore mine site. The fungi was utilised for dissolution of manganese from the low grade manganiferous ore. Leaching with the biomass free culture filtrate and with various acids such as oxalic, citric and sulphuric acid, provide a better insight to the process. On the basis of these studies, kinetic equations as a function of time is plotted to obtain appropriate conversion-time equation for leaching of manganese ore with bioacid and organic acid. The experimental values showed that the reaction is controlled by diffusion of the reactants through the permeable product layer. (C) 2003 Elsevier Ltd. All rights reserved.