The influence of oral temperature on the orthodontic force of a super-elastic Ni-Ti alloy wire was investigated by three-point bending test. The temperature change at the wire slot of the bracket on the upper first molar ranges between 7 and 52℃. Therefore, force change was measured under conditions of temperature change between 3 and 60℃. The load was measured at the point of 1.0 mm deflection. The load in the loading process decreased slightly through the temperature change of 37-60-37℃ and 37-3-37℃. The load in the unloading process increased considerably through the temperature change. Thermal cycling affected the load alternately both in the loading and unloading process. It was proven that the orthodontic force of the super-elastic Ni-Ti alloy wire changes in a complicated manner by the temperature change in mouth, and that the load changes even after the temperature recovers.