Since the disposal of sewage sludge in ocean has been prohibited recently according to London Dumping Convention, technological need for treating sewage sludge safely and efficiently are getting increased in Korea. FBC (Fluidized Bed Combustor) technology has been selected and utilized as one of the alternatives because of combustible content in sludge, on-going process development to maintain the best combustion efficiency, and good heat recovery for energy utilization. In this paper, the process and combustion characteristics of commercially operating FBC incineration plants with the capacity ranging from 50 – 150 tons of sludge per day were investigated by comparing emission data from 4 different plants. Concentrations of hazardous gaseous pollutants (HAPs) such as fine particulate matter, heavy metals, and dioxin from sludge combustion before and after air pollution control devices were measured and analyzed at commercial operating conditions of one typical incinerator. Most of emission data at stack showed under the environmental regulatory limits. Mercury and some heavy metals emission have been reduced significantly as co-beneficial effect since the air pollution control configuration was well arranged and installed to control the regulatory gases such as NOx, SO2, particulates, and dioxin. Sludge, especially generated from industrial plants, contained measurable amounts of acidic materials and heavy metals including Hg. Therefore, such metal emission should receive an attention by monitoring them and further mass balance study for better understanding their fates in the process must proceed in future