Abstract <p>Several constitutive models were constructed to predict the flow stress behavior of Zircaloy-4 in hot working, and the best constitutive model was identified. For this purpose, a Gleeble-3500 thermo-mechanical simulator was used to perform isothermal uniaxial compression tests in the range of strain rates and deformation temperatures of 0.001–1 s^–1 and 750–1000°C, and the true stress-strain curves were obtained. Using the experimental data, the modified Johnson–Cook model, strain-compensated Arrhenius-type model, modified Zerilli–Armstrong model, and microstructure-based model were developed for α single phase field and α + β two phase field, respectively. The correlation coefficient and the average absolute relative error were 0.9979 and 3.61% for the microstructure-based model, 0.9912 and 7.01% for the modified Zerilli–Armstrong model, 0.9821 and 12.24% for the modified Johnson–Cook model, and 0.9857 and 10.31% for the strain-compensated Arrhenius-type model, respectively. The results show that the microstructure-based model is able to accurately predict the hot deformation behavior of Zircaloy-4.</p>