A seawater hydraulic actuator system for a subsea robot has been developed. The system consists of a high pressure axial piston pump, flow control servo valves and actuators which transform controlled flow into motion, and it is very effective in miniaturizing a subsea robot. In order to confirm overall characteristics of this power system, a prototype tele-manipulator for underwater work has been also developed. A manipulator control system is based on a master-slave method with some telepresence technique to provide an easy operation of a manipulator. Through running experiments in underwater manipulation, overall characteristics of the seawater hydraulic system and working performance of the prototype subsea manipulator have been confirmed to be good enough for practical use.