Abstract: A biomimetic manta ray robot fish actuated by shape memory alloy (SMA) wires is presented. The robot fish is propelled by oscillation of a pair of flexible pectoral fins, and swims like a kind of rajiform model. Firstly, swimming characteristic of manta ray is analyzed and a simple kinematic model of manta ray flexible pectoral fin is built. Secondly, the intelligent materials for simulating the muscle motion of manta ray are analyzed. Finally, the flexible biomimetic pectoral fin actuated by SMA wires, the biomimetic manta ray robot fish is developed, and the thermodynamics analysis on SMA wire is performed to optimize the control rule of SMA wire. The biomimetic manta ray robot fish is similar to manta ray in shape. It also has a flat-form body and a pair of triangular flexible pectoral fins. Its maximal swimming speed in line is 79 mm/s. Its minimum turning radius is 118 mm. It can swim stealthily with good stability.