The liquidus surface of the Al–Ti–Pt system has been constructed for the first time on the composition triangle based on studies of the structure and phase composition and measurement of the liquidus temperatures for the as-cast alloys in the composition range 0–50 at.% Pt produced using a series of techniques. The liquidus surface has 23 primary crystallization fields corresponding to τ1–τ9 and τ11 ternary phases and binary phases formed in the boundary systems and to solid solutions based on components. The extension of these fields and the positions of univariant curves and invariant points have been determined. The liquidus surface exists in the temperature range from 1830°C (corresponding to congruent melting of TiPt compound) to 655°C (temperature of the l ⇄ <Al> + <Al21Pt5> eutectic in the binary Al–Pt system).