Dioxins, which include polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (co-PCBs), are chlorinated organic compounds with high toxicity. In this study, detoxification of dioxins was carried out in a solution of NaOH in 2-propanol in the presence of an alumina-supported palladium catalyst (Pd/Al₂O₃). When dioxins were extracted from fly ash, which had been collected in a commercial solid-waste incinerator, and were treated by using this system at 82 °C for 3 h, the concentrations of dioxin homologues decreased nearly to the experimentally detectable limits. The toxicity reduction was calculated to be > 99.96 %. We studied the reaction mechanism and revealed that chlorine atoms of dioxins were replaced stepwise by a hydrogen atom of 2-propanol and consequently dioxins were transformed to chlorine-free compounds.