Transformation of mercury compounds in combustion flue gas and overall mercury mass balance in a typical bituminous coal-fired power plant were studied Upon decreasing temperature and interaction with flue gas components, oxidized mercury increased across an electrostatic precipitator. A major fraction of particulate mercury was removed in the electrostatic precipitator, and oxidized mercury was removed in wet flue gas desulfurization Hg was mainly speciated into elemental form in the stack emission The measurement of mercury in a real facility and equilibrium calculation showed that coal composition, operating conditions, and flue gas components were the major factors affecting mercury emission and speciation A reliable overall Hg mass balance was obtained from the field measurement. Mercury mainly entered from coal, and lime/limestone feeding was distributed in electrostatic precipitator fly ash (57 6-64.3%), gypsum (4.5-12.9%). effluents (0 5-1 9%), and stack emission (15 2-27 0%) Further, the mass distribution and speciation of mercury in the power plant with simulated coal mixture feeds could be predicted with a chemical equilibrium code in combination with the measured results at the commercial plant.