The results obtained in this study indicate that addition of sulfur in incineration processes could effectively reduce PCDD/F formation. PCDD/F formation is reduced dramatically (54.1%) when S/Cl molar ratio is controlled at about 2 in a laboratory-scale system (LSS). The XRD analysis of the fly ash confirms the existence of vulcanized metals such as Cu2SO4, Cu2S, SnS and ZnS. The results suggest that the sulfur added would poison Cu-based metals and render the Deacon reaction catalyst less active, thereby reducing PCDD/F formation. In addition, the results obtained from the tests conducted in an industrial waste incinerator (IWI) indicate that the efficiency of reducing PCDD/F formation by adding sulfur was 51.6% at S/Cl mole ratio of 0.4. The results indicate that adding too much sulfur would actually increase particle concentration and also increase PCDD/F yield. This study demonstrates the effectiveness of adding sulfur as an alternative technology for reducing PCDD/F emissions from waste incineration processes. The efficiency of reducing PCDD/F formation by addition of sulfur is strongly influenced by S/Cl mole ratio.