sampling and analysis of mercury at inlet and outlet of air pollution control devices (APCDs) have been conducted to provide information on mercury speciation, mass distribution and removal. Two municipal waste incinerators and two industrial waste incinerators, each with dry and wet types of APCDs, and two cement kilns were selected to measure mercury concentrations mainly at stacks, as well as selected locations between the APCDs. Gaseous sampling was implemented in accordance with the Ontario Hydro (OH) method to determine whether mercury forms were elemental or oxidized. Mercury removal efficiencies were relatively higher with more than 70% due to tight APCDs configuration. Oxidized mercury was dominant in municipal solid waste incinerators. Due to high collection of particles by filters, higher mercury removal efficiency was observed at the incinerator with dry type APCDs. Such behavior was confirmed by the results of mass distribution of mercury, which showed most of mercury in fly ash in case of the incinerator with dry type APCDs. By passing through the APCDs, the portion of the oxidized form of mercury seemed to increase in most cases because of increased contact time with the flue gas and fly ash and/or enhancing the mercury oxidation rate by acidic gas components. The mercury removal efficiencies in the industrial waste incinerators in this investigation were lower than those in the municipal waste incinerators due to less tight APCDs configuration, and because the speciation and fate of mercury between two types of APCDs (wet and dry) were quite different. In wet type APCDs, the oxidized mercury was removed by absorption to water at the scrubber since Hg2+ is soluble in water. For cement kilns, more elemental mercury was formed and emitted from kilns as shown only 24-31% of oxidized mercury at the inlet of APCDs, which is opposite behavior with the previous results from incinerators. The higher temperature of kiln furnace and lower concentrations of oxidizing components such as chlorine and oxygen than that of incinerators might have caused it. Our study revealed mercury emissions and speciation depend on the factors as Hg concentration in the industrial wastes, type of APCDs, flue gas composition and temperature. Mass balance of mercury in the process was attempted to determine from the emission data and analysis results of mercury at all the in- and out-streams such as waste feed and effluents from APCDs. An approximate Hg mass balance was obtained based on various samples collected, however a series of long term and comprehensive study would be required to evaluate the reliable Hg distribution at waste incinerators.