This article describes the chemical properties of the resulting ash from co-combustion of hard coal with biomass. Biomass consisted of sunflower husks, bran grains, and forest biomass. To test the fly ash we sampled from different types of boilers: pulverized, fluidized, and in the case of pulverized boilers ash samples with and without desulfurization products were tested. The results were compared with the properties of ash without co-combustion, which were obtained in the same type of boilers. Chemical and mineralogical compositions were determined and thermal analysis was carried out as well. Studies showed no effect of co-combustion biomass with coal on the tested properties of obtained ash.