Accurate description of the material flow stress behaviour is an essential requirement for FEM simulation of metal forming processes. In the present hot compression tests of AZ80 magnesium alloy were performed on Gleeble 3500 at strain rates between 0.01-50s-1 and deformation temperatures between 300-450°C to determine the flow stress data of the AZ80 magnesium alloy. It was noticed that with increasing strain rate, deformation heating become more pronounced since there is no time for heat escaping during hot compression tests. Thus, a flow stress correction for deformation heating at high strain rates was carried out for the calculation of the constants of constitutive equation. Validation tests were then performed. Good agreements between the predicted and measured values in extrusion pressure were achieved.