In this study, the characterization and microstructure observation of the sintering behaviour of F (from Seyitomer Thermal Power Plant) and C (from Soma Thermal Power Plant) types fly ashes, red mud and red mud-fly ash mixtures at 4 and 8 h milling times with a mortar type ball are investigated. The particle size distribution (PSD) was carried out by laser technique. The PSD analysis revealed that the particle size decreased with increasing milling time. After milling, the samples were pressed into a cylindrical form without using any additive or binder. The formed samples were sintered at 1050 degrees C. Phase evolutions and microstructures of the formed samples were carried out by using X-ray diffraction method (XRD) and scanning electron microscope (SEM) method, respectively. The water absorption and compressive strength were tested to determine some physico-mechanical properties. The results of mineralogical analysis as well as the microstructural observations reveal that phase transformations occurred during the sintering treatments. The results showed that at the chosen optimum conditions (F type fly ash-red mud mixture with 1:1 ratio, sintering temperature of 1050 degrees C and milling time of 4 h), the best characteristics of sintered glass ceramic could be obtained. Values obtained from mechanical testing showed that the fly ash-red mud sintered ceramic materials had increased strength compared to other sintered ceramic materials. The sintered materials from red mud have the highest water absorption value.