By means of the CALPHAD (CALculation of PHAse Diagram) technique, the Pt–Zr system was critically assessed. The solution phases (liquid, bcc, fcc and hcp) are described with the substitutional model. The intermetllic compounds Pt 4 Zr, Pt 4 Zr 3 , αPtZr and Pt 3 Zr 5 are treated as the formula (Pt,Zr) m (Pt,Zr) n by a two-sublattice model with the elements Pt and Zr on the first and the second sublattices, respectively. A two-sublattice model (Pt,Zr) 0.5 (Pt,Zr) 0.5 is applied to describe the compound βPtZr with CsCl-type structure (B2) in order to cope with the order–disorder transition between bcc solution (A2) and βPtZr (B2). Another two-sublattice model (Pt,Zr) 0.75 (Pt,Zr) 0.25 with Ni 3 Ti-type structure (D0 24 ) is applied to describe the compound Pt 3 Zr in order to cope with the order–disorder transition between hexagonal close-packed (A3) and Pt 3 Zr (D0 24 ). The compound Pt 10 Zr 7 is treated as a stoichiometric compound. A set of self-consistent thermodynamic parameters of the Pt–Zr system was obtained.