The purpose of this study was to reduce the dioxin content of fly ash from an incinerator by thermal treatment. To increase the residence time of fly ash in the incinerator, the fly ash was mixed with different amounts of coal and clay and then pelletized. All experiments were conducted in a bench-scale fluidized bed combustion system. The polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs) content of the fly ash were investigated following combustion. The results showed that the I-TEQ (Toxic Equivalents Quantity of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin) values of the ash collected from the cyclone met Taiwan's regulatory standards (< 1 ng g–1). The total toxicity of dioxin, including those in the fly and bottom ash, can be reduced by 88–95% after combustion. The strength of the pellets is enhanced by the addition of clay, resulting in their aggregation in the bed and discharge as bottom ash. The distribution profiles of the PCDD/Fs homologs in the fly ash collected from the baghouse in each experiment were similar. The most prevalent congeners in the ash were 1,2,3,4,6,7,8-HpCDF, OCDD, and OCDF. The predominant contributor to the total I-TEQ values was 2,3,4,7,8-PeCDF. The amount of residual carbon in the fly ash is strongly correlated with the dioxin content of the fly ash collected from the baghouse.