Abstract: The time-dependent unified hardening constitutive model for overconsolidated clays (time-dependent UH model) proposed by the authors is extended to a constitutive model considering K₀-anisotropy. Based on the generalized non-linear strength criterion and the corresponding transformed stress tensor, the new model is generalized to the three-dimensional stress state. The new model is then used to predict one-dimensional and triaxial CRS (constant rate of strain) tests on K₀-consolidated clays. The predicted results indicate that the new model can reflect reasonably the influence of strain rate on preconsolidation pressure and stress-strain relationship of K₀-consolidated clays. Moreover, a theoretical function of triaxial undrained shear strength is deduced from basic equations of the new model. The calculated results of the theoretical function are compared with the experimental ones, and it is shown that the theoretical function can describe the experimental phenomenon that triaxial undrained strength increases with the increasing overconsolidation degree or the strain rate.