Abstract: This paper discusses a widely used rate-dependent concrete model in which the viscosity parameter is related with strain rate. A rate-dependent model, which is developed based on elastic/viscoplastic theory employing the overstress concept, is proposed in order to verify and compare the previously-proposed rate-dependent concrete model. The analytical solutions to the governing differential equations of the two different models are presented under the constant strain rate loading, stress relaxation and creep conditions, respectively. Theoretical and numerical comparison between the two models is given. It is demonstrated that the previously-proposed model is invalid theoretically and,results in significant numerical error during the transient response state. At the same time, it is shown that the proposed rate-dependent model is capable of describing the material responses at the various loading conditions unanimously.