A fish-like robot boat has been built to simulate fish swimming dynamics. This robot boat uses oscillating plate swimming mode as it uses only single oscillating tail fin. Several experiments have been carried out to provide sufficient data to be processed for the identification process. The experiment data are collected by using an inertial measurement unit (IMU) which consists of three gyroscopes and three accelerometers. A mathematical model, a transfer function between the swimming direction and the fin's mean angle of oscillation, is obtained from the data and identification algorithm. The identified model approximates the real system quite well. This model has been used to design PID directional controller for the fish-like robot