The 450 ∘ C isothermal section of the Al–P–Zn ternary system has been determined using optical microscopy, scanning electronic microscopy coupled with energy dispersive x-ray spectroscopy, and x-ray diffractometry. No true ternary compound was found in the present study. The optimized descriptions of the phase diagram and thermodynamic properties of the Al–P and P–Zn binary systems were obtained from experimental data by means of the CALPHAD technique. On the basis of the literature data for thermodynamic assessment of Al–Zn and the present work on Al–P and P–Zn systems, the phase diagram calculation for Al–P–Zn was carried out. A consistent set of thermodynamic parameters for each phase was derived. The optimized results and the experimental data are in good agreement.