a b s t r a c tThe solid-state phase equilibria in the Co-Pt-Tb ternary system at 1173 K (Tb ≤ 70%) were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) techniques. The 1173 K isothermal section consists of 14 single-phase regions, 25 two-phase regions and 12 three-phase regions. At 1173 K, we have observed that the maximum solubility of Tb in ␣-(Co, Pt) is below 1.5 at.%Tb, with the maximum solid solubility of Pt in the compounds Co 17 Tb 2 , Co 7 Tb 2 , Co 3 Tb and Co 2 Tb being below 1 at.%Pt, 2 at.%Pt, 3.5 at.%Pt and 2 at.%Pt, respectively. Furthermore, the maximum solid solubility of Co in the compounds Pt 5 Tb, Pt 3 Tb, Pt 4 Tb 3 , PtTb, Pt 4 Tb 5 , Pt 3 Tb 5 , PtTb 2 and PtTb 3 is below 1 at.%Co, whereas in Pt 2 Tb it reaches 17 at.%Co. With the introduction of Co, the Pt 4 Tb 3 phase gradually decomposes into the two neighboring compounds PtTb and Pt 2 Tb, while with the Co content exceeded 9 at.%Co, the Pt 4 Tb 3 phase disappears. No new ternary compounds or Co 5 Tb were observed in our study.