In order to increase the performance and the reliability for several kind of nozzle in jet cutting, fuel injection, atomization and so on, the microscopic internal structures of high-speed water-jets were carefully visualized by using techniques of a laser light sheet and laser holographies. The free jets discharged from a small nozzle, 1.11mm in diameter, were injected into the non-restricted atmosphere. The ruptured processes of water columns, which play an important role in the abilities of jet-cuttings and fuel injections, are clearly shown.