In this paper, we describe on the results of our investigation on a stern flow field of a ship in oblique towing motion. The purpose of this investigation is to get basic data necessary and available for developing, improving and verifying an estimation method of hydrodynamic forces acting on a ship in manoeuvring motion. We used three VLCC model ships. They have almost same principal dimensions but different stern shapes. One ship has a V shaped stern, another ship has an U shaped stern, and the other ship has a medium shape stern between the V and the U shaped stern. Kinds of experiments that we did are measurement of flow field by 5 hole Pitot tube, observation of flow field by tuft and measurement of hydrodynamic forces acting on a model ship. By these experiments, we investigated characteristics of flow field around a ship in oblique towing motion, and discussed relation among stern shape, flow field and hydrodynamic forces. There is no big difference qualitatively among stern flow field of these three model ships in oblique towing motion, characteristics of which are represented by two groups of separating vortices. However, there are clear differences in strength, concentration and range of distribution of wake and vorticity among three model ships. Concerning to hydrodynamic forces acting on a model ship in oblique towing motion, there is little difference in magnitude itself of hydrodynamic forces, but there is a clear difference in center of pressure that has a serious effect on a ship manoeuvrability. These results will be useful data for framing a flow model, developing, improving and verification of estimation method of flow field and hydrodynamic forces, and for examination of ship stern shape.