Analysis techniques for quantifying crystal structures of mineral phases and their fractions in iron ore sinters have been developed using the Rietveld analysis of X-ray diffraction patterns and applied to iron ore sinters of different mechanical strength, which were prepared by laboratory-scale sinter pot testing. The Rietveld analysis successfully determined the phase fractions and structural parameters for co-existing phases such as hematite (α-Fe₂O₃), magnetite (Fe₃O₄), multi-component calcium ferrites or silico-ferrite of calcium, and aluminum (SFCA:Ca₂(Ca,Fe,Al)₆(Fe,Al,Si)₆O₂₀ and SFCA-I:Ca₃(Ca,Fe)(Fe,Al)₁₆O₂₈) and other minor phases. The strength of the iron ore sinter correlated with the quantity of magnetite and not simply with that of the calcium ferrites determined by this method. The lattice constants of calcium ferrites differed among the specimens; moreover, no clear difference was observed among iron oxide phases. These results show that the Rietveld analysis provides crucial information for controlling the sintering process and suggests the phase fractions.