Remarkable developments in Diesel engines have been made in seventy years since the first unit was successfully tested in the shop of M. A. N. in Augusburg, Germany in 1897. In Japan, the Nagasaki Works of the Mitsubishi Shipbuilding Co., Ltd. designed and manufactured the first Diesel engine in 1917. Since then, many other companies in Japan completed their own designs and have incorporated various improvements. The author makes a historical review of the technical developments of Diesel engines in Japan, and describes major researches and experiments made on the basic problems of Diesel engines in relation to the practical application during the process of development of Diesel engine. The development of the MS type two-stroke cycle Diesel engines in 1932 and investigations on various problems related to scavenging methods, fuel injection systems, exhaust turbo-chargers, thermal stresses and temperature distributions in cylinder liners and pistons, photo-elastic expemiments on engine construction, rigidity of engine beds, design of bearing, exhaust valve driving gears, and non-cooling turbo-chargers, etc. are included. Researches for up-rating of Diesel engines and processes of developments of Vee-form Diesel engines are also explained. The future possibility of manufacturing of Diesel engines of very large size type is stated in the conclusions.