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An equiatomic CuZr alloy quenched from 1073 K was studied by isothermal mechanical spectroscopy and X-Ray diffraction. Experiments were performed using a very large frequency range (10-4Hz – 50 Hz) at different temperatures. For each temperature of measurement, experiment started after complete microstructure stabilization of the sample. At room temperature, the X–Ray diffraction spectrum shows that there are two CuZr monoclinic phases as a consequence of a martensitic transformation. These structures are characterized by the existence of twinning defects for the first one and a high dislocation density for the other. Both monoclinic phases disappear at higher temperatures and first transform into the cubic CuZr phase, then this cubic phase transforms into Cu10Zr7and CuZr2phases above 763 K. Internal friction spectra exhibit two relaxation peaks (P1, P2), at low and high temperatures, respectively. After rapid cooling of the sample from 1273 K, the first peak P1appears from room temperature and disappears after annealing above 673 K. The P2peak appears at about 800 K and increases for measurements at higher temperature up to 880 K. This temperature range corresponds with the existence of both Cu10Zr7and CuZr2phases. These two peaks are associated with a relaxation linked to the dislocation microstructure in the two CuZr monoclinic phases for P1 and in the Cu10Zr7and CuZr2phases for P2.