Coal ashes and ash-and-slag mixture, produced by the power stations and piled vastly in ash disposal areas, contain valuable chemical elements utilized in some important industries. The data on the chemical composition of these samples need to be acquired prior to recovering the appropriate elements. To determine the basic components in ashes, such as Na 2 O, MgO, Al 2 O 3, SiO 2 , P 2 O 5 , K 2 O, CaO, TiO 2 , MnO and Fe 2 O 3 , the X-ray fluorescence spectrometry ( XRF ) is frequently used. Samples are prepared as glass disks fused from the mixed coal ash and flux. However, high dilution ratios and high temperature in the fusion process prevent the determination of some micro and volatile elements, e.g. S, Ga, Sc and Co, etc. Current paper reports a fast and less time-consuming XRF procedure to simultaneously determine the basic components and microelements in fly ashes, coal ashes and ash-and-slag mixture. The samples are prepared by pressing the tablets from the powder ash material on the boric acid backing. In addition to the aforementioned element oxides, S, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Y, Nb, Ba and Pb contents are evaluated in the coal combustion products produced by the power stations in Irkutsk Region and Buryatia Republic. The line and background intensities are measured using the S4 Pioneer (Bruker, Germany) wavelength x-ray spectrometer. The errors in XRF results are found to vary from 1 to 12 in major elements and from 12% to 28% in microelements. As it turned out, the errors were due to the inhomogeneous phase composition of the samples. The detection limit values varied within 0.010 to0.030 in oxides and from 0.0005 to 0.0030 % mass in microelements. Keywords : x-ray fluorescence spectrometry, coal ash, ash-and-slag mixture, major oxides and microelements DOI: http://dx.doi.org/10.15826/analitika.2017.21.3.011 E.V. Chuparina 1 , L.Ph. Paradina 2 1 Vinogradov Institute of Geochemistry SB RAS, 1A Favorsky St., Irkutsk, 664033, Russian Federation 2 Limnological Institute SB RAS, 3 Ulan-Batorskaya Street, Irkutsk, 664033, Russian Federation