The focus of this study is the effects of sulfur and calcium compounds on reducing dioxins in fly ash collected from the baghouse of a pilot-scale fluidized bed combustor. Pelletized sawdust with various amounts of polyvinyl chloride (PVC), pyrite, and calcium hydroxide was used as the feeding material. The experimental results indicated an extremely low concentration of dioxin in the fly ash from the cyclone (0.025 to 0.284 ng g–1), and the concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the fly ash collected from the baghouse increased by 27.4% as the chlorine content increased from 0.568 to 1.136 wt%. The inhibition of PCDD/Fs by sulfur is not clear and can be attributed to the low content of copper (average 387 ppm), which serves as the catalyst for the Deacon reaction. Octa-chlorinated dibenzofuran (OCDF) was the major congener of the PCDD/Fs. The highest toxicity-equivalent (I-TEQ) of 2,3,7,8-substituted congeners was 2,3,4,7,8-PeCDF, which accounted for 37% of the total congeners (average value). The correlation between the I-TEQ values and 2,3,4,7,8-PeCDF concentration of fly ash is also discussed.