To overcome the global warming by CO 2 emission, charging ratio of scrap for BOF should increase in future. Usually metallurgical coke is added to increase the melting capacity of scrap in BOF. Compare with the heat efficiency of the reaction of carbon in molten steel with top blown oxygen gas, the combustion of coke on molten slag is not good. Therefore, the added coke has to contact with molten steel for carburization. However, due to the poor wettability between slag and coke, it is difficult to emulsify the coke in slag. By the research in the ironmaking field, it was known that the wettability between liquid and solid affects on the liquid flow. Since the surface structure of coke changes as the reaction of carbon with CO 2 or iron oxide, motion of slag with coke may change depending on the change in physical property of coke surface. In the present study, to investigate the influence of the surface structure of coke, sliding angle, and advancing and receding contact angles of droplet on coke substrate were investigated. Water and mercury, and the SiO 2 -CaO-Al 2 O 3 melt were employed as liquid sample for the measurements at room and high temperature, respectively. The surface structure of the coke substrate was varied by heating in CO-CO 2 or CO 2 atmospheres at 1273 K. Larger irregularities of coke change little the motion of droplet. However, it was found that the fine irregularities on the surface of coke substrate reacted with CO 2 gas decrease the sliding angle of droplet and increasing dynamic contact angles. This tendency was observed for all the liquid samples. The irregularity is caused by gasification reaction of carbon and distribution of ash. A possibility was shown that slag flow with coke can be promoted by controlling the property of metallurgical coke.