PFBC is one of the two important advanced fossil fuel technologies, now available. It permits the combustion of fossil fuels with extremely low emissions, while also achieving high electrical conversion efficiencies. However, relatively little is known about the ash characteristics, despite the existence of several demonstration units. This study looks at bed and cyclone ash from two of these boilers, the Spanish PFBC plant at Escatron, in Spain, and the Tidd plant in Brilliant, Ohio. In particular, these ashes are examined using both conventional and some newly developed techniques in order to determine their chemical speciation. This work confirms the ashes have extremely low free lime contents (1% or less), and extremely low elemental carbon. More surprisingly, the existence of significant amounts of dolomite in the cyclone ashes from the Tidd plant has been demonstrated, and significant quantities of other calcium compounds (i.e. silicates, ferrites etc.) have also been shown in the bed ashes from the Spanish plant. One other interesting observation is the presence of low levels of sulphides in the ashes from the Escatron unit, and its total absence from the Tidd unit which used dolomite rather than calcitic limestone. These results also clearly indicate that ashes from PFBC plants are likely to be significantly easier to dispose of in landfills than AFBC ashes, and should have considerably better potential for use in cementitious applications.