ABSTRACT Turret moored floating body, such as FPSO, FSRU and FSU weathervanes on a turret according to wave, current and wind. Turret moored body can oscillate from side to side or move to one particular direction, and eventually shows large yaw motion. The yaw of turret moored vessel is one of factor to affect the motion performance, mooring load and offloading operation. In tandem and side-by-side configuration, yaw is more important which influences STS (Ship To Ship) mooring, operation possibility (downtime). It is necessary that the behavior of yaw is known for the design of mooring system and the assessment of operability and safety. In order to investigate the behavior of yaw, analytic study and experiment were carried out at MOREI's ocean engineering basin. In this study, vessel is moored by internal turret and mooring lines. Experiments were done for regular wave conditions and the characteristics of yaw were analyzed for the period of waves. Experimental results show that the excessive yaw occurs to maximum 50 deg. The static stability was also investigated by analytic method. The stability analysis is verified by comparing with experimental results. It is confirmed that the turret moored body have the unstable and large yaw in particular wave period.