The development and field application of the environment friendly Precast concrete by replacing the blast furnace slag were examined. As a result, it was found that compressive strength of Precast concrete used 50% of blast furnace slag was similar to Plain. While 70% of blast furnace slag was slightly decreased. In the result of Mock-up Test, the compressive strength of Precast concrete used 50% of blast furnace slag was satisfied with the target strength. but greening phenomenon occurred. Although greening occurred on the surface of the Precast concrete, it was gradually disappeared over the age. Therefore, the use of blast furnace slag was available up to 50%.