This work describes the effect of mechanical working and heat treatment on the microstructure of the alloy Ti-13Nb-13Zr using X-ray diffraction and metallography. Lattice parameters of the constituent phases in as cast and different heat-treated conditions have been calculated. The β solution treatment and water quenching (WQ) results in the α′ martensite while the α + β solution treatment and WQ leads to three-phase microstructures consisting of α″, α and β. Only α and β phases are observed under aged condition irrespective of the prior solution treatment conditions. The effect of various heat-treatments on the hardness of the alloy has been presented. © 2001 Elsevier Science B.V. All rights reserved.