The phase diagram of the Al-Cu-Zn ternary system was re-investigated experimentally. The current study was designed to contribute to a better description of those parts of the phase diagram, which are disputed in the current scientific literature. Mutual relations in the family of ternary intermetallic phases tau with cubic, rhombohedral and modulated structure at temperatures 400 degrees C and 550 degrees C were described. The phase relation between the gamma and gamma ' phases was studied at different temperatures. A two-phase field between gamma and gamma ' was observed below 400 degrees C, while the transition appears to be second order at higher temperatures. A vertical section between gamma and gamma ' phases in Cu-Zn and Al-Cu and four isothermal sections at 400 degrees C, 550 degrees C, 700 degrees C and 820 degrees C, respectively, were constructed.