Ash sintering may cause problems in fluidized bed combustors. It may contribute to both bed agglomeration in the furnace of the FBC, as well as to deposit formation in the cyclone and plugging of the cyclone return leg. The sintering process may be promoted by a molten phase present in the ash. In this paper, we compare the sintering tendency of an ash with the melting behavior of the same ash. The sintering tendency was measured by a laboratory test method based on compression strength measurements, and the melting behavior was evaluated with a multicomponent, multiphase equilibrium model. Ten biomass ashes were chosen for the study. The compression strength test showed significant differences in the measured sintering tendencies for the various ashes. The comparison between the measured sintering tendencies and the melting behavior calculations revealed that in 7 cases out of 10, an estimated amount of some 15% molten phase present in the ash may have been the reason to the increased degree of sintering in the tested ash pellets.