The final goal of this study is to realize three-dimensional maneuverability, a characteristic of fast swimming animals such as dolphins, with a biomimetic robot. As the first step towards this goal, a dolphin robot with a body length of 1 m was developed and loop-the-loop motion experiments were conducted. In order to stabilize the roll angle of the dolphin robot, the control algorithm for the joints of the dorsal and pectoral fins was examined by numerical simulation. From the simulation, it was found that the conventional PD control with regard to the roll angle is sufficient for this control. The dolphin robot could stabilize the roll motion in the experiment, too. Next, the motion of the dolphin robot was measured by a three-dimensional motion analysis system. The radius of the loop-the-loop motion was found to be 0.5m, which is half the body length of the dolphin robot.