The author studied the scavenging of crank case compression type two stroke cycle diesel engines, and examined the influences of engine speeds, delivery ratios, fuel injection quantities, crank case compression ratios and guide angles of scavenging ports upon the scavenging performance. Furthermore these engines were remodeled into the type with a scavenging pump and compared with the former. Thus the scavenging characteristics of crank case compression type two stroke cycle diesel engines were made clear.