High-temperature (≈ 900−1400 K) steady-state creep test data on as-received zirconium alloys, Zr-1wt%Nb and Zircaloy-4 used as fuel cladding materials in light water reactors are evaluated by employing two sets of models. In particular, the focus of the paper is on the former alloy and in the two-phase coexistence region, i.e. the (α+β)-domain of the alloy. In one modeling approach, the constitutive relations for the two single phase regions (α and β) are combined through a phase transition kinetic model and a phase mixing rule; in another, a superplasticity model is used directly to calculate the creep deformation rate as a function of stress and temperature in the (α+β)-domain. The results show that the former approach is inadequate in retrodicting the experimental data, while the latter one gives a fair overall agreement. The paper describes the details of the models, the data, and derivations of the constitutive laws.