A coke oven battery is not considered as a significantsource of polychlorinated diben-zo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) emissions; how-ever, due to small amounts of chlorine in coal dioxins, dibenzofurans may be formed. The paper presents the attempts to determine the level of emission of PCDDs/PCDFs from the COB underfiringsystem and to confront the obtained results with the cal-culations based on the mass balance of chlorine in the coking process and reactions of both chlorophenols formation and PCDDs and PCDFs formation from mono- and polychlorophenols. There were PCDDs/PCDFs concentrations measured in fluegases from the underfiringsystem of two COBs at a Polish coking plant. The measure-ments included both an old and a new battery. The obtained concentrations of PCDDs/PCDFs were lower than reported in the literature (0.5–1.7 ng I-TEQ/Mgcoke), while the results for old COB were on average 3 times higher than for the new one. It was found that PCDDs/PCDFs emission from COB underfiringsystem is insignificantand that PCDDs/PCDFs formation during coal coking should consider the mechanisms of their formation from mono- and polychlorophenols, as well as the influenceof process parameters on the synthesis.