Combustion characteristics of Refuse Derived Fuel (RDF) were investigated by using an experimental circulating fluidized bed combustor with a riser of 0.108 m inner diameter and 6 m height at various temperature and air bias ratios. The following results were obtained: (i) HCl concentration in the flue gas was kept at a very low level under all operating conditions by De-HCI of calcium contained in RDF; and (2) unburned carbon in the fly ash was also at a very low level because of its good combustibility. Concerning the NO and N2O, it was found that N2O emission was low under all operating conditions, but that NO emission was slightly high under single stage combustion and reduced at 50% bias ratio. SO2 emission was not detected because of the low sulfur content and high calcium content in the RDF.