The role of tin as a solid solution strengthener and a precipitation hardener in zirconium base alloys has been examined. Mechanical properties and microstructure of Zr-Sn binary (0.5 to 8 wt% Sn) alloys were investigated in both β-quenched and tempered conditions. The yield and ultimate tensile stresses and the percentage elongation were evaluated as a function of tin content, C, in both β-quenched and tempered Zr-Sn alloys. The 0.2% yield stress shows a linear relationship with C^2/3, suggesting the operation of the Mott-Nabarro model of solid solution strengthening in which clustering of solute atoms is envisaged. The presence of tin solute clusters could also be detected in TEM microstructures of β-quenched alloys. The effect of tin content on the yield and flow behavior of zirconium has been examined at temperatures between 77 and 673 K. Results indicate that the addition of tin influenced both the thermal and athermal components of flow stress. The activation volume was found to be independent of the plastic strain, while it showed an increase with temperature and a decrease with solute content. The deformation process appeared to be controlled by two ratecontrolling mechanisms: (a) dislocations overcoming the substitutional solute clusters at temperatures below 473 K, and (b) movement of jogged screw dislocations at higher temperatures. The intermetallic precipitate phase formed due to tempering was identified as Zr₃Sn with A15 structure having the following orientation relationship with the matrix: (0001)α//(111)Zr3Sn <1210>α//<231>Zr3Sn Because of the good lattice registry between the precipitate and the matrix phases, partial coherency between them is maintained even after considerable growth of precipitate particles.