Floating turbines are attracting increasing interest today. However, the power generation efficiency of a floating turbine is highly dependent on its motion stability in sea water. This issue is more marked, particularly when the floating turbines operate in relatively shallow water. In order to address this issue, a new concept motion stabilizer is studied in this paper. It is a completely passive device consisting of a number of heave plates. The plates are connected to the foundation of the floating wind turbine via structural arms. Since the heave plates are completely, rather than partially, exposed to water, all surfaces of them can be fully utilized to create the damping forces required to stabilize the floating wind turbine. Moreover, their stabilizing effect can be further amplified due to the application of the structural arms. This is because torques will be generated by the damping forces via the structural arms, and then applied to stabilizing the floating turbine. To verify the proposed concept motion stabilizer, its practical effectiveness on motion reduction is investigated in this paper. Both numerical and experimental testing results have shown that after using the proposed concept stabilizer, the motion stability of the floating turbine has been successfully improved over a wide range of wave periods even in relatively shallow water. Moreover, the comparison has shown that the stabilizer is more effective in stabilizing the floating wind turbine than single heave plate does. This suggests that the proposed concept stabilizer may provide a potentially viable solution for stabilizing floating wind turbines.