Decrease of carbon dioxide emission is a serious subject in the steel industry. Although low reducing agent operation of blast furnace is a primary method in ironmaking, many different ways should be taken. Utilization of biomass as a carbon-neutral reducing agent is an attractive one for ironmaking. However, since the calorific value is relatively low as an injection material and the oxygen content derived from the functional group is higher than coal, the direct injection of raw biomass into the blast furnace is not favorable. Optimized carbonization of biomass is proposed to keep high carbon yield and to attain selective oxygen removal by controlling the atmosphere, heating time and temperature condition. In carbonization, it was clarified that the carbonization of biomass from 300 to 500°C in the inert gas atmosphere improves the replacement ratio of coke and the crushability by intentionally changing the biomass composition and structure. It was estimated that the combustibility of the carbonized biomass became similar to pulverized coal. The effect of carbonized biomass injection into blast furnace was estimated with Rist diagram. The injection of biomass carbonized in the optimized condition effectively decreases CO₂ emission from the ironmaking process.