The briquett-samples containing Fe_2O_3. SiO_2 and CaO were heated at 1, 200℃ and 1, 300℃ in the atmosphere of air or of mixed gas of CO and CO_2 so that the iron oxides might occur as hematite or magnetite or wustite. These samples were deoxidized with CO or H_2 at 900℃, and their reducibility, expressed as a value of comparative reducibility, was determined from their own reduction curve. The influence of composition of raw materials and of sintering atmosphere on reducibility was confirmed. Their porosity was determined, and also the relation between reducibility and porosity was discussed. The results obtained from this investigation were as follows ; in the atmosphere of air, SiO_2 and CaO contents of iron oxide materials seemed to have little effect on reducibility of iron oxide, and it appears that reducibility varied directly with porosity when iron oxide mixtures were heated at 1, 200℃, but there was found no longer such a clear relationship when heated at 1, 300℃. In the reducing atmosphere, even a little amount of SiO_2 in the iron oxide materials gave undesirable effect on reducibility, and addition of CaO together with SiO_2 could not so much recover it as decreased it, till CaO was added enough for the content of SiO_2. There was found no direct relationship between reducibility and porosity, and the more reducing the atmosphere was more evident the tendency became
