We developed a conceptual feasible design of bioreactor system for treatment of dioxin-contaminated soils that uses the dioxin-degrading fungus Pseudallescheria boydii (P. boydii) we had isolated. The dioxin-degradation conditions in bioreactor treatment was established by clarifying the inhibiting factors for the growth of P. boydii using both real contaminated and laboratory prepared soils mixed with fly ash. In addition, ethanol extraction process as post-treatment methods for the remaining dioxins, and the sterilization conditions of P. boydii, i.e., a weakly pathogenic fungus, in the residue was investigated. The better growth conditions of P. boydii were found to be chloride ion concentration of less than 10 g/L and a pH of less than 9. Under these conditions, 73 10 pg-TEQ/g of the soil was treated to 2860 pg-TEQ/g by the bioreactor process, and the dioxin concentration was further decreased to 580 pg-TEQ/g by ethanol extraction, resulting to total removal ratio of 92%. Furthermore, development of an effective sterilization method for living P. boydii in the residue increased the applicability of our bioreactor system for practical use in dioxin-contaminated sites. (C) 2007 Elsevier B.V. All rights; reserved.