Recently, R&D of marine renewable energy becomes very popular all over the world. In this paper, the contra-rotating turbines are adopted as an ocean current power generator. The contra-rotating turbine system is theoretically torque free, since the second blade counters the first blade torque. Therefore, small main body (pod) and low cost mooring might be achieved. In this paper, a conceptual design of the contra-rotating ocean current turbine is presented. A computer code, which represents motions of the pod and turbines with 6 degrees of freedom together with the non-linear mooring effect, is developed. The numerical results are compared with experiment in which a newly developed small size turbine-generator model is used. The results show that the current turbine is stably moored even when the flow direction is suddenly changed. An attempt to reduce the pod motion by controlling the blade pitch angle is also discussed and it is found that it could be possible to reduce both long and short period unsteady motions.Summarizing these results, it is concluded that the contra-rotating ocean current turbine has a technical merit from the perspective of motion characteristics.