In thermochemical utilization of biomass, ash fusion temperature is an important parameter for the efficient and continuous operation of boilers/gasifiers and high value-added utilization of the ash. Fusion characteristics and transformation properties of the inorganic components in biomass ash are investigated using X-ray fluorescence (XRF), thermal gravimetric analyzer (TGA), X-ray diffraction (XRD), ash melting point test system and phase diagrams. XRF and TGA results show the changes of ash content, elemental composition and performance with the variation of temperature. Two main weight loss routes of biomass ash, decomposition and volatilization, are identified. XRD results show the transformation behavior of crystalline structure of different biomass ash. Intense internal reactions that occur in biomass ash at higher temperature generate a large amount of eutectic compounds, which lowered the melting point significantly. The contribution of different ash compositions to fusion can be assessed by binary diagrams while the fusion properties of silica-rich biomass ashes obtained by phase diagrams could be appropriate for industrial running. (C) 2013 Elsevier Ltd. All rights reserved.