The progressive trend in material-intensive industries is the use of industrial waste as raw materials suitable for the industrial industry. One of such wastes is ash microspheres, which are a by-product of the operation of solid-fuel thermal power stations. Comparison of the properties of the ash microspheres of different manufacturers by their physicochemical, morphological, dielectric and other properties allows to comprehensively evaluate each sample of the material. On the basis of this evaluation, it is possible to select the assignment of ash microspheres, which would maximally effectively use their potential in the composition of the composite material. For the study, ash microspheres obtained at various TPSs of Ukraine: Trypillia, Burshtyn, Kurakhove, Kryvyi Rig and Prydniprovska are selected. As a result of studies of the mineralogical composition, structure and properties of ash microspheres, it is found that the latter are a high-temperature material with a high temperature resistance. The specific surface of the ash microspheres is comparatively small and depends, in the main, on the mineral constituent of the coal rock. Thus, for the investigated materials the effective specific surface area varies within the limits of 1.7–2.3 m 2 /g. As for the mineralogical composition, the predominant crystallophase is represented, mainly mullite (91–98 %). An exception in this case is the ash microspheres of the Kurakhove TPS, in which mullite is 43 %. Also, a significant proportion of the mineralogical composition of the ash microspheres of the Kurakhove TPS is opal cristobalite (37 %). Also, the thermal conductivity of ash microspheres of selected TPSs in Ukraine is investigated. The highest coefficient of thermal conductivity is the ash microspheres obtained from the Trypillia and Burshtyn TPSs (0.190 and 0.184 W/(m·K), respectively), and the lowest – Prydniprovska TPS. Ash microspheres serve as a promising material both from the point of view of processing coal waste and from the point of view of using it as filler for building materials with increased thermal insulation properties. From this it follows that ash microspheres allow to significantly expand the scope of their use, including in the construction industry.