The isothermal section of the Co–Pt–Dy system at 773 K was experimentally determined by combining results from X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy investigations. The presence of Co 3 Dy 4 phase at 773 K is confirmed in this study. The four-phase region does not exist at 773 K in the ternary Co–Pt–Dy system, with instead two three-phase regions consisting of Co, DyPt, Dy 3 Pt 4 and Co, DyPt 2 , Dy 3 Pt 4 , respectively. 23 single-phase regions (including solid solution regions of the binary compounds) and 21 three-phase regions were identified to exist at this isothermal section. The highest solid solubility of Dy in α1(Co, Pt), ∊(Co, Pt), α2(Co, Pt), CoPt, CoPt, α(Pt, Co) is less than 1.5 at.% Dy and that of Co in Dy 3 Pt, Dy 2 Pt, Dy 5 Pt 3 , Dy 5 Pt 4 , DyPt, Dy 3 Pt 4 , DyPt 3 , DyPt 5 is below 1 at.% Co. The DyPt 2 phase dissolves up to about 19 at.% Co. The maximum solid solubility of Pt in Co 2 Dy, Co 3 Dy, Co 7 Dy 2 , Co 17 Dy 2 is approximately 1 at.% Pt. No new binary and ternary phases were found.