The Soma power plant in western Turkey consists of six 165-MW units (B1-4 and B5-6) and two small 22-MW units (A1- 2), the first four units (B1-4) of which burn Early-Middle Miocene feed coals from the lower seam in central mines (southern Soma village), two units (B5-6) use Early-Middle Miocene and Upper Miocene feed coals from the lower and upper seams in Denis mines (northern Soma village), and the later unit A burns relatively clean coals after a washing plant from the lower seam in central mines. Characterization and chemistry of fly ashes in hoppers 1 and 2 from unit B1, and hoppers 1-4 from unit B5 have been studied to determine the variation in fly ash constituents/compositions between the two units. Twenty-four fly ash samples were collected from the hoppers in an array of electrostatic precipitators at 12 h intervals in two days. Data of proximate analysis showed that the fly ash samples have very low volatile matter contents and very high ash yields, as we expected. The ash yield in unit B1 slightly increases from coarser particles (hopper 1) to finer fly ash particles (hopper 2). Lower increase has been also detected in hoppers 1-4 of unit B5. X-ray diffraction (XRD) traces of six fly ash samples selected from each hopper showed that the forming minerals and phases are glass and quartz, the major minerals and phases include lime, anorthite, mullite, anhydrite, hematite, while the minor and accessory minerals are portlandite and gehlenite. Slightly greater contents of lime, portlandite and gehlenite, and lower contents of quartz have been determined in hoppers of unit B1 than in hoppers of unit B5. Results of elemental analysis showed that unit B5 has greater concentrations of Al, Na, K, Ti, Fe, S, As, B, Ba, Be, Bi, Cd, Co, Cr, Cs, Cu, Ga, Ge, Hf, Li, Mo, Nb, Ni, Pb, Rb, Sb, Sn, Ta, Th, Tl, V, W, Y, Zn, Zr, REEs, and lower concentrations of Ca and U than unit B1. Despite these distinctions the mean values for Mg, P, Mn, Sc, and Sr do not show significant variations in the two units. In addition, the mean values for hoppers in both units indicate that some volatile element concentrations, notably As, B, Bi, Cd, Pb, Zn, increases from coarse to finer particle size fly ashes. This implies that the Soma fly ash has variations between units B1 and B5, depending on feed coals and combustion conditions.