[Abstract]The reduction of dioxins in exhaust gases is an important issue on combustion treatment of waste organic liquids and waste municipal solids. In this study, the reduction of dioxins was examined on waste liquids treatment processes. The facilities employed (called as In-liquid combustion system) were semi-continuous systems on a daily basis and waste organic liquids were combusted or decomposed in furnaces at higher temperature (above 800℃). The gases from furnaces were directly sprayed in a water tank (a reaction vessel) and gas temperature was cooled down under 100℃. The gases were further treated through a gas scrubber, a stack, and an adsorption column for mercury gas. The water used for both cooling and cleaning of gas was treated using wastewater treatment processes containing a sand filtration column, an activated carbon column, and a chelate-resin column. The results obtained were as follows: The concentration of dioxins in exhaust gases was very low. Especially, combustion at high temperature and longer residence time of gas were effective for the reduction of dioxins. The concentrations of HCl, SOx, and dust in exhaust gases were low. Dioxins trapped in water were effectively removed by the wastewater treatment processes and the results obtained were as follows: 1) Dioxins in water existed almost in a particulate form and not in a dissolved form. 2) The concentrations of dioxins decreased rapidly by use of a sand filtration, an activated carbon, column, and chelate-resin column. 3) Thus, dioxins were hardly found in final treated waters.