Steelmaking slag is one of the main by-products of steelmaking process,and approximately 13 million tons of BOF slag are generated annually in Japan.Ironmaking and steelmaking slags have to be effectively utilized for the development of sustainable steelmaking process.In Japan,most of steelmaking slag is recycled as civil engineering materials and so on.Since the demand of steelmaking slag as construction materials is expected to decrease with the formation of developed society,the recycling use of slags becomes important issues.Two schemes should be considered to solve the issues of steelmaking slag,first one is to reduce the amount of slag generation by the improvement of refining processes and second one is to find the new application way of steelmaking slag in other fields by adding the new functional properties.Recently,steelmaking slags are utilized as the rehabilitation materials for marine environment.In the present paper,the present situation of slag generation and previous and present research projects regarding slag utilization in Japan are introduced and the possibility of utilization of slag for rehabilitation materials of marine environment as a new recycling technology is discussed.Some fundamental experimental results conducted in our research group are also introduced.