To examine the characters of the scavenging air flow through the scavenging ports in two-stroke engines, the inlet flow pattern through the model ports has been observed by a high speed motion camera, using a single cycle test apparatus. In general, the scavenging air flow is not coincident with the designed direction of the scavenging port at comparatively slight opening, and the efflux direction changes with the piston displacement. In a small crankcase-scavenged two-stroke engine cylinder, to keep the scavenging air flow close to the direction of the scavenging port it is effective to make the scavenge air guide long and to incline the scavenge air passage between the crankcase and the cylinder axially along the circular surface of the cylinder. In a large loop scavenged engine cylinder, to make the scavenging air flow coincide with the direction of the scavenging port in the early stage of scavenging, it is effective to set the guide plate inside the scavenging port.