SynopsisFor a stable operation of blast furnace and a decrease in fuel rate, the improvement of the qualities of sinter which is the principal charging material is very important. At Wakamatsu Sinter Plant of Nippon Steel Corporation which is equipped with a double-layer charging system, the plant experiment has been made to improve the reducibility of sinter by making uniform and ideal heat pattern in the sintering bed. In this experiment, sinter with excellent properties, 3.7 % FeO, 70 % JIS RI, good hightemperature properties has been manufactured. Findings obtained are summarized as follows:(1) An effective means o f improving the sinter reducibility is to cause porous ore to remain as unmelted ore by lowering the sintering temperature at about 1 250 to 1 300 °C and by increasing the temperature-rise rate in the high-temperature zone.(2) Compact ore should have fine grains to improve the sinter reducibility.(3) The reduction degradation index (RDI) of sinter can be improved by reducing the ratio of A1203JSiO2 in fine raw mix and by lowering the sintering temperature.