Abstract <p>A comprehensive study is performed to investigate the effect of zinc concentration on structural and phase transformations in metastable (α + β) Cu-Zn-based shape memory alloys. The start and finish temperatures of forward and reverse martensitic transformations in Cu-<i>x</i>Zn alloys (<i>x</i>=38, 39.5, and 41 wt %) are determined using electrical resistance measurements. Structure and phase transformations are studied by optical, scanning and transmission electron microscopy as well as by X-ray phase analysis. It is found that critical temperatures of thermoelastic martensitic transformations decrease with an increase in the zinc concentration. Diffuse effects in the selected area electron diffraction patterns are analyzed depending on the zinc concentration in metastable Cu-Zn binary alloys. An increase is observed in the dislocation density under thermal cycling due to the martensitic transition.</p>