The objective of this work is to improve carbon burn-up during plastic incineration in fluidized bed incinerators, since unburned hydrocarbons and carbon particles in the exhaust gas are considered to be sources of dioxins. The influence of bed material on carbon burn-up and hydrocarbon emission during plastic pellet combustion was investigated by using several kinds of porous particles. For comparison, quartz sand was used as a conventional bed material. Plastic combustion and plastic pyrolysis were investigated using a fixed bed reactor. The former showed an improved carbon burn-up to CO2 and the latter carbon deposition for porous particles. During experiments using a bubbling fluidized bed combustor, the influence of the bed materials on the carbon burn-up and the horizontal concentration profile above the dense bed were investigated. For the porous particles tested, the improved carbon burn-up to CO2 and a uniform horizontal concentration profile above the dense bed were observed. These were explained by improved horizontal distribution and prolonged residence time in the dense bed due to carbon deposition onto the porous particles.