An experimental investigation has been conducted to study the dynamic constitutive behavior of Hastelloy X (AMS 5754) at room and elevated temperatures under varying rates of loading. A split Hopkinson pressure bar (SHPB) apparatus was used in conjunction with an induction coil heating system for applying dynamic loads at elevated temperatures. Experiments were carried out at different temperatures ranging from room temperature (25 A degrees C) to 1,100 A degrees C at an average strain rate of 5000/s. Room temperature experiments were carried out at varying strain rates from 1000 to 4000/s. The results show that as the strain rate increases from quasi-static to 4000/s, the yield strength increases by approximately 50%. Also, under dynamic loading, the yield stress decreases with temperature up to 700 A degrees C, after which it shows a peak at 900 A degrees C before beginning to decrease again as the temperature is further increased. The Johnson-Cook model was used to predict the dynamic plastic response under varying rates of loading and at different temperatures.