Fluidized bed combustion of high ash anthracite (HAA) was experimentally studied. The combustor consists of 0.25m ID bed, and auxiliary equipments for coal feeding, ash removal, temperature control, etc, Experimental results elucidate main cause of fuel loss to be elutriation of fines(i.e., flyash) containing unburned carbon. However, detailed balances of particle size distribution show majority of carbon in flyash comes from fines contained in the feed instead of attrition of coarse particles. The latter is the main source of flyash for conventional coal. The difference is due to much smaller attrition rate of HAA; feed HAA particles do not shrink much in size by combustion and attrition.