In this paper low voltage single crystal actuators were investigated using thin PMN-PT plates for applications requiring low voltage, large strain, low profile and/or actuation at cryogenic temperatures. Firstly, single crystal thickness effect on piezoelectric properties was studied by investigating the relationship between electromechanical coupling coefficient of PMN-PT crystals and the crystal thickness. It was found that electromechanical coupling coefficient (kt) of 50 μm, 75 μm and 100 μm PMN-PT single crystal thin plates are 0.5, 0.51, and 0.55, respectively, which are slightly lower than that of bulk single crystal (0.6). A couple of single crystal actuators were then assembled using crystal plates with thickness of 150-200 μm. These actuators were characterized by measuring strain vs. electric field at room temperature and cryogenic temperatures. A 3 mm x 3 mm x 19 mm single crystal stack actuator showed a 21 μm stroke at room temperature under 150 V, and a 10 μm stroke at 60 K under 200 V. A 5 mm x 5 mm x 12 mm single crystal actuator showed 13.5 μm stroke at room temperature under 150 V, and 6 μm stroke at 77 K under 150 V. These low voltage actuators hold promising for space precise positioning and adaptive structures and cryogenic SEM, SPM and STM applications.