Fish type underwater robots has a lot of possibilities such as good mobility and high efficiency. Most of the fish type robots developed up to now have complicated mechanisms with complicated motion control. It results in that the structure and the movement of robots are different from that of fishes. The purpose of our work is to develop creature-like flexible underwater robots by using piezoelectric fiber composite. Compared with conventional artificial muscular underwater robots, powerful underwater robots with a very simple structure can be composed. This paper describes the development of a flexible underwater robot with caudal fin propulsion, which can generate large propulsive force and move at high speed. Besides, by utilizing the large propulsive force, pitch and roll motions are realized by attaching two pectoral fins to the robot.