The strength of sintered ores is an important property affecting to the permeability of the ore layers of the blast furnace. Since the granulated ores have a composite structure with coarse ores coated by fine ores, melting behavior of those ores is complex including a stepwise melting during sintering. Therefore, it is difficult to predict precisely the strength of sintered ores particularly in the case of ore mixtures consisting with many types of ores. Hence, a prediction method for the strength of sintered ores obtained by mixing several types of ores was investigated. By assuming stepwise melt formation process, two different experimental techniques were adopted to individually evaluate the melting behaviors. The strengthening characteristics of fine ores were effectively expressed by the penetrating length. The penetrating length was reflected by the melt fluidity during heating and depended on the quantity of gangue minerals and combined water, as well as the initial grain size of the ores. In contrast, the strength of sintered coarse ores was expressed by the total porosity after melting with limestone. The total porosity depended on the quantity of combined water and types of gangue minerals. As the governing factors in the melt formation of fine ores and coarse ores were different, the quantitative indices of them were estimated individually and re-combined as the sinter strength index to predict the characteristics of the whole ores mixtures. Results of pot tests revealed that the index correlated well with the measured strength of sintered ores.