Abstract: Abstract: In the past decades, sustainable development and increasing fuel demand have necessitated the identification of possible energy sources. The utilization of biomass will reach up to 50 million tons in China after ten years. Nowadays, many countries are putting great emphasis on the exploration of biomass energy. The techniques used are various such as combustion, gasification, pyrolysis, hydrogen production. The use of the biomass as fuel generates a large amount of residual ash which causes serious environmental problems, as the biomass ash is easy to melt and volatilize. During the thermo-chemical conversion process, the residual inorganic materials also form the slag inside the boiler and the fly ash deposits on the tail heating surface, which retards heat transfer, deteriorates burning, and causes high temperature corrosion and super heat explosion. As one kind of clean and renewable energy, rice husk (RH) and rice straw (RS) are the main by-products during the process of rice processing. Especially, in comparison with other agricultural wastes, the ash content of RH is much higher. After thermo-chemical conversion, the inorganic mineral matters left are ashes, which can easily bond with tar and lead to the phenomenon of slagging, fouling and corrosion for the thermo-chemical conversion equipments. Therefore, in this study, the analysis of microstructure characteristics and elemental composition of these ashes from the combustion of RH and RS at 600℃ and 815℃ respectively was comprehensively conducted by using the scanning electron microscopy (SEM) and the energy dispersive X-ray microanalysis (EDX). The influence of ashing temperature on the particle size distribution, micromorphology, particle surface, interior structure and elemental composition of biomass ash was investigated. The results showed that the higher the ashing temperature was, the smaller the size of the ash would be. With the increase of ashing temperature, the distribution of ash was more homogeneous. A majority of rounded particles were found in the rice husk ash (RHA), while most of rod-like particles were found in the rice straw ash (RSA). For the 600℃ RHA, part of the ash particles still retained the original fiber structure of rice husk, and some dense granules were observed which had no sticking phenomenon. Whereas, plenty of floccule that was adhered to by many small particles existed in the 600℃ RSA, which indicated that the weak caking occurred which was caused by the melting of the constituents with low melting point. Molten alkali metal material and quartz structure in the form of vitreous bumps were found on the surface of 815℃ ash particles, which presented obvious reunion slagging phenomenon. The main composition elements of RHA and RSA were carbon (C), oxygen (O), silicon (Si), potassium (K) and calcium (Ca). Magnesium (Mg), aluminum (Al), iron (Fe) and phosphorus (P) which had only a small quantity were also detected. The element surphur (S) was only detected in the RSA, which was not detected in the RHA. With the increase of ashing temperature, the K content of RHA obviously decreased. But for RSA, the content of K, sodium (Na) and Ca changed slightly while the content of chlorine (Cl), Fe and Al decreased obviously. The K, Na, Ca and Cl contents of RSA were much higher than those of RHA, which indicated that the RSA was much easier to cause equipment corrosion than the RHA. This work reveals the effects of ashing conditions on the microstructure characteristics and elemental composition of RHA and RSA comprehensively, and can provide the guidance not only for preventing slagging, fouling and corrosion in the thermo-chemical conversion equipments, but also for the clean burning of biomass and comprehensive utilization of both RHA and RSA.