This article describes the zinc leaching of-fly ash from municipal waste incineration by the thermophilic archaean Acidianus brierleyi. In the bioleaching system, inorganic acid, sulfuric acid, was biologically produced from elemental sulfur added to liquid medium and simultaneously used to leach zinc in the fly ash. Leaching experiments with A. growing on elemental sulfur were performed to determine effects of various process parameters on the leaching rate of zinc in the fly ash Under the conditions determined as optimum, the biobleaching of fly ash by A. brierleyi yielded 90% extraction of zinc in 9 days of batch operation at an initial ash-liquid loading ratio of 1.0 kg/m(3) and an initial sulfur-liquid loading ratio of 5.0 kg/m(3).