The effect of activated carbon (AC) injection on control of mercury emission from a fluidized bed type municipal solid waste incinerator (FB-MSWI) was investigated in two actual FB-MSWIs. Furthermore, lab-scale experiments were conducted to confirm the results of the field tests. In the field tests, Hg concentration at the outlet of the bag filter was reduced to less than 0.002 Mg/m(N)(3) by injecting AC of 50 Mg/m(N)(3). In the lab-scale experiments, The Hg reduction ratio of fly ash with activated carbon was 50% higher than that of fly ash without activated carbon. No difference in Hgreduction ratio was found between AC concentrations of 50 Mg/m(N)(3) and 100 Mg/m(N)(3). With FB-MSWI fly ash, it was easier to remove mercuric chloride than metallic mercury. This characteristic of FB-MSWI fly ash was different from that of stoker type MSWI fly ash. This difference was estimated to be caused by the composition of fly ash, especially the contents of copper and iron.