The influence of hydrogen sorption-desorption cycles on defect structure of Zr-1Nb alloy was investigated. Specimens were hydroganated from gas atmosphere at temperature 500 °C and pressure 2 atm up to the hydrogen concentration equal to 0.05 wt.% for each cycle. The hydrogen concentration during saturation was determinate by the volumetric method. Then samples were annealed at temperature 900 °C with the heating rate of 4 °C/s. The lattice defects were studied by means of positron lifetime spectroscopy (PLS) and doppler broadening spectroscopy (DBS). New experimental data about the evolution of the average positron lifetieme τavg, as well as the relative changes in the parameters S, W depending treatment stage in Zr-1Nb alloy during thermo hydrogen proccessing was obtained.