The feasibility of extracting metal values from the oil sands fly ash has been studied in some detail; however, little work has been completed on the mineral phases in the fly ash and their phase changes during ash formation from oil sands coke. Characterization of the ash is essential to obtain sufficient information about the mineral assemblage and its processability. In this study, coke obtained from Syncrude and Suncor, which are the two major oil producers in northern Alberta, Canada, was investigated to elucidate the morphology, ash formation behavior, and the mineralogy, by ashing it at various temperatures. Both high temperature ashing and low temperature ashing (LTA) were employed, and the ash structure was investigated using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The results clearly showed that a slight difference in chemistry and mineralogy between two samples greatly affected the properties of ash at high temperatures. Formation of oil sands fly ash was explained by the movement of iron-titanium-related minerals and amorphous aluminosilicate melts.