Diatomaceous earth is an effective carrier with a large surface area on which Thiobacillus ferrooxidans adsorbs, and enhances the oxidation rate of ferrous ions by the bacterium. The adsorption of T. ferrooxidans on diatomaceous earth was expressed by the Henry isotherm, and reached equilibrium within five minutes. The enhancement was due to an Increase in the growth rate of the adsorbed cells, which were so active that their specific growth, rate calculated using a Monod-type equation was higher than that of the free cells in the liquid phase.