Comparative studies of industrial fly ash from coal and biomass co-combustion (50%: mixture of sunflower pellets, wood chips, and straw briquettes) and coal ash were conducted. The functional speciation of metals (Pb, Cd, Zn, Cu) and mobility of chemical fractions of ash (soluble in water, exchangeable, soluble in acids pH5, oxide, pseudosulfide, residual) were carried out with a 6-stage sequential extraction and singlestage mineralization methods. It was found that the addition of biomass to coal results in ash containing more Zn, a decrease in the content of Cd, and no major changes in total content of Pb and Cu. A mixture of sunflower pellets, wood chips, and straw briquettes added to coal as biomass results in an increase of the ash fractions: exchangeable (Pb), pseudosulfide (Pb, Cu), oxide and residual (Zn), reduction in ash fractions: soluble in acid pH5 (Pb, Cd, Zn), oxide (Cu), pseudosulfide (Zn), residual (Cd). Biomass co-combusted with coal (50/50 m/m) improves the ash by reduction of the environmental mobility of Pb, Cd and Zn, but does not cause major changes in the mobility of Cu in relation to coal ash.