A kinetic study of the batch leaching of a pyrrhotite ore by a sulfooxidans strain is reported in this work. A mathematical model consistent with experimental data is developed, which takes into account both direct and indirect mechanism. The development has been performed from a separate study of microorganisms' adsorption on the solid surface and of chemical leaching of pyrrhotite by ferric iron. The representative equations of these phenomena (Langmuir equation and a kinetic model with variable activation energy, respectively) have been combined with material balances of total iron, ferric iron and biomass. The final model consists of a system of three ordinary differential equations, where the independent variable is time and dependent variables are total iron, ferric iron and biomass concentrations in solution. The key parameters of the model were: the specific growth rate, mu(A), the growth yield, Y-A' of adsorbed bacteria, and the reaction rate constant of ferrous iron oxidation, k. These parameters were estimated by curve fitting using experimental data and estimated values (mu(A) = 1.34 +/- 0.02 d(-1), Y-A' = 3.6 +/- 0.3 x 10(13) cells/mol, k = 0.229 +/- 0.004 d(-1)) are in agreement with values found in the literature.