Abstract The room temperature section of the phase equilibrium diagram of the Al-Cr-Cu ternary system has been investigated by means of X-ray powder diffraction method. Beside the single phases of the three binary systems, there exist five new phases in the diagram, which we call ω1, ω2,εf, εx, and γx phase, so that the diagram of the system is divided into 19 single-phase regions, 41 two-phase regions, and 22 three-phase regions.The new phase γx has an orthorhombic cell, its diffraction pattern is similar to that of γ2. By comparing with that of γ2, we find that some strong diffraction lines are absent in γx, and some other strong diffraction lines exist, therefore the crystal structure of γx differs from cubic, and has an orthorhombic cell. It exists in such a narrow region, that it may probably be a compound.The other new phases ω1 and ω2 are very similar to each other in their feature. The new phase εf has a comparatively wide range in composition, and it seems to change rather continuously in its diffraction pattern as the composition is changed. On the other hand, the new phase εx has only a small region, and the diffraction pattern is completely diffrent from that of the other new phases.