It is well known that the occurrence of the defects has a close relation with the behavior of the bubbles and the flow pattern of the molten steel inside the mold. In this research, the behavior of argon gas inside the flowing water and the influence of wettability between the water and the porous refractory through which argon gas is injected were investigated. In addition, the influence of the wettability on the behavior of injected gas in molten iron was investigated experimentally. Furthermore, a water model simulating the submerged entry nozzle and the mold of the continuous casting process was established. The behavior of argon gas that was injected into water flow through a porous refractory in nozzle and its influence on the flow pattern of the water inside the mold were studied in the cases of different wettability between water and the porous refractory. Water model experiment demonstrated quite different behaviors of the bubbles and flow pattern of water when the wettability was changed. The result in the case of poor wettability is thought to be similar to those of the continuous casting process in which molten steel does not wet the refractory.