At Keihin No. 1 Blast Furnace, waste plastics recycling system was installed in Oct. 1996. Before the installation of that system, the behavior of waste plastics injected into the blast furnace has been studied with the raceway hot model and the commercial blast furnace so as to investigate the possibility of effective waste plastics utilization in the blast furnace. From the observation of plastics particle injected into the raceway of blast furnace, it was estimated that combustibility of coarse plastics was much different from that of pulverized coal. The combustion point of coarse plastics located to deep domain in raceway compared with that of pulverized coal. Although C₁ –C₄ hydrocarbons due to the decomposition of plastics was detected in in-furnace, the decomposition products of plastics in the blast furnace top gas and dust were the same as that of pulverized coal injection. The preparation method of plastics had an influence on the combustion and gasification behavior in the raceway. The coarse plastics gave high combustion and gasification efficiency compared with fine plastics and pulverized coal, and CO₂ gasification rate of unburnt char derived from waste plastics was much higher than that of pulverized coal. Thus, it was concluded that coarse waste plastics could be effectively utilized as a reducing agent in the blast furnace. On the basis of above results, the waste plastics recycling system was designed.