Abstract A phasediagram of the alloys of the dysprosium-copper binary system has been determined by means of X-ray diffraction and differential thermal analysis techniques. Its constitutional diagram has been constructed. Two eutectic reactions occur at 12 and 83 wt%Cu approximately, and with characteristic temperatures of 808 and 88°C, respectively. At room temperature three stable intermetallic compounds have been found, namely DyCu, DyCu2 and DyCu5. The DyCu and DyCu2 are formed by peritectic reactions at 840 and 885°C respectively, and DyCu5 melt congruently at 97°C. However, another intermetallic compound DyCur forms at 89°C periteetically and decomposes eutectoidally at 848°C as it is cooling slowly. The solid solubility of Dy in Cu is undetectable, and the solid solubility of Cu in Dy is less than 0.2 wt%Cu at room temperature.