This paper presents a fundamental study on the mixture formation process in a direct injection stratified charge (DISC) engine. Helium is injected intermittently and impinged on a wall to clarify the unsteady wall impinging jet. Instantaneous concentration and pressure distributions are obtained by using fast-response concentration and pressure probes, respectively. The jet tip rolls up after the impingement on the wall, consequently the volume of an unsteady wall impinging jet becomes larger than that of a steady wall impinging jet. Wall impingement increases air entrainment, which could promote faster combustion in DISC engines.