The strain rate effect of engineering materials should be considered in the assessment of the performance of reinforced concrete (RC) structures under extreme dynamic loads such as blast and impact. However, the strain rate behavior of 500 MPa-grade anti-earthquake hot-rolled high-strength ribbed bar (HRB500E), used in critical RC members to improve the anti-earthquake performance, has not been investigated and reported in the open literature. That restricts its application in RC structures subjected to extreme dynamic loads. In this paper, dynamic tensile tests of HRB500E steel were conducted using an electromechanical universal testing machine and a servo-hydraulic high-speed testing machine. The stress-strain curves at strain rates ranging from 0.00025 to 550 s were obtained where HRB500E steel was found significantly sensitive to strain rate. Existing formulations to evaluate the dynamic increase factor for yield stress (DIF) are found to be not suitable for HRB500E steel, thus the widely used Cowper-Symonds and Malvar models for predicting the DIF were modified based on the test results. Furthermore, the parameter of the Mander material model for describing engineering stress-strain relationship was also calibrated. Finally, the Johnson-Cook and proposed constitutive models for the true stress-strain relationship were examined. The proposed constitutive model can provide better prediction accuracy for yield stress than the Johnson-Cook model.