The fly ash leaves the combustion zone with the off-gas and is separated from the off-gas by dust separators. For the handling and treatment of fly ash its chemical composition and physical properties are important. Fly ashes from biomass combustion slightly contaminated with heavy metal can be utilized as a soil conditioner, thus closing the nutrient cycles for the soil where the biomass was grown. In this study five cyclone fly ashes from grate-fired bio mass combustion plants were investigated. Most of the fly ashes showed poor flowability, especially the fly ashes with small particle size. The flowability of the fly ash from straw combustion was also poor although this fly ash is rather coarse. This is probably caused by longish remainders of incompletely combusted straw stalks in this fly ash. All fly ashes contain valuable nutrients for the soil. However, in all fly ash samples from wood chip combustion the measured concentrations of Cd and Zn were above the limit concentration. Therefore, these fly ashes cannot be used as soil conditioners. The fly ashes from straw combustion and from palm oil residue combustion were much less contaminated by heavy metals and can be utilized as soil conditioner.