The objective of this study was to realize the backstroke with the swimming humanoid robot. By realizing the backstroke, the backstroke performance of the robot was assessed regarding the speed and the swimming behavior. The motion for the robot was generated based on the motion of an actual swimmer. However, since the robot did not have sufficient degreesof-freedom to realize the motion, the actual motion was modified. The motion was investigated by simulation and later by the experiment. In the experiment, the robot successfully realized the backstroke at the stroke cycle 2.3 s with a swimming speed of 0.28 m/s.