The influence of tin content on the unirradiated mechanical properties of zirconium alloys within the Zircaloy-4 specification has been analyzed. A cold-worked, stress-relieved (CWSR) commercial cladding was produced using similar thermo-mechanical processing encompassing tin contents ranging from 1.22 to 1.54%. Thermal creep testing, tension testing, contractile strain ratio (CSR) testing, and texture analysis were preformed over the range of tin contents. Creep testing was performed at 399°C (750°F), over a series of stress ratios and stress levels. The creep strength of Zircaloy-4 was strongly dependent on the tin content over the allowable composition range. The effect of tin was dependent on the stress state, with the 0:1 stress ratio (hoop stress:axial stress ratio) and 1:1 stress ratio showing greater effects than 2:1 stress ratio. The steady state strain rates increased by factors of 6, 5, and 2 for the 0:1, 1:1, and 2:1 stress states, respectively, as the tin content decreased toward the lower tin content limit of 1.20%. A generalized multiaxjal thermal creep equation was used to model the influence of tin content and to separate the anisotropy and stress dependence. The stress dependence and thermal activation energy were insensitive to alloy content; however, the anisotropy parameters measured under low strain rate conditions moved closer to isotropic conditions as the tin content decreased. It was concluded that the change in the creep anisotropy was due to a change in the predominant slip system from a predominantly basal slip at high tin contents to a mixed basal-prism slip at low tin contents.