The characteristic of green sand changes as it is heated by pouring. Then, after experimental repeated pouring, the green sand composition, and its properties were measured, and the penetration defect caused in a test casting was detected. As a result, it became evident that the sea coal in green sand changed the condition by the heat influence. That is, the sea coal powder changed to adhere to sand surface as the total clay removal. After heating, the oolitics increased, the specimen density increased, and the scabbing time decreased. The penetration defect became difficult to occur when volatile matter in sea coal was more and ash in sea coal was less.
