Abstract: Abstract: The installed capacity of power plants directly firing agricultural and forestry biomass is increasing rapidly in China. As a consequence, the annual production of biomass ash, as a by-product, from the power plants increases greatly. Ash management and utilization is becoming an important issue to consider in daily operation of power plants. Biomass ash from grate-fired power plants includes bottom ash and fly ash. In comparison to bottom ash, fly ash may have higher contents of hazardous and toxic heavy metal elements enriched during biomass combustion process. The potential impact of heavy metals on the environment may limit its applications for agricultural and forestry purposes. It therefore necessitates comprehensively characterizing the properties and evaluating the potential environmental impact of fly ash before its utilizations. In this work, we aimed to investigate the utilization of biomass fly ashes from grate-fired power plants for agricultural and forest purposes and their environmental impact. Two fly ashes (A and B) were respectively collected from two grate-fired power plants, both burning mixed fuels of crop straws and wood barks. The ashes were characterized systematically with various methods. Based on the analysis results, their applications on agricultural and forest soils and corresponding environmental impact were evaluated based on the relevant standards. Following standard methods, the basic properties of the two fly ashes including the contents of moisture, content of ash and total organic carbon, the pH value, electrical conductivity and their size cuts were measured. The contents of nutrient and heavy metal elements were determined with inductively coupled plasma-optical emission spectroscopy and inductively coupled plasma-mass spectroscopy, respectively. For evaluating the environmental impact, the leaching behavior of the fly ashes was also analyzed following the national standard of solid waste-extraction procedure for leaching toxicity. The results showed that both the fly ashes were strongly alkaline with the pH values greater than 12. They were high in total organic carbon content (18.39% and 7.79% for ash A and B, respectively) and rich in nutrient elements including K, Ca, Mg and P. Both ashes were lower in heavy metal elements and their contents of the main heavy metal elements were below the limits set by the standards of some European countries for utilizing biomass ashes on agricultural and forestry soils and by China national standard for using coal fly ashes. The high pH value and Ca content implied that the two ashes could be used as soil conditioner. The high content carbons of the two ashes were beneficial to improve soil quality. Nevertheless, the contents of K2O plusP2O5 were 9.62% and 6.04% for fly ash A and B, respectively, much lower than those required for compound fertilizer. However, it did not exclude their use as soil conditioner materials of compound fertilizer on soils. In all, the two fly ashes can be used as a fertilizer or soil conditioner in agriculture and forest. The characterization on the size cuts of the two ashes suggested that the application may even be improved by pre-treating the ashes with size fractionation. Moreover, the leaching of the main heavy metals in the fly ashes were , much lower than 1% except 1.274% for Cr in fly ash A. Thus the utilization was not likely to pollute the agricultural or forest soil.