Thermal behaviour of raw fly ashes-wasted products from various Polish power plants has been investigated using X-ray diffractions (XRD), Fourier transform infrared spectroscopic (FT-IR), differential thermal analysis (DTA) and thermogravimetry (TG). On the basis of the DTA and TG analysis differentiation between examined ashes has been made, which could not be achieved by XRD and FT-IR methods.