By the methods of differential thermal, X-ray, microscopy and electron microprobe analysis phase equilibria in the Tirich corner of the Ti–Si –Al system were studied. Projections of solidus and liquidus surfaces as well as an isothermal section at 1300 °C were constructed. It was shown that at the solidus and 1300 °C Ti 5 (Si,Al) 3 (Z) phase coexists with all of the Ti– Al-based phases, resulting in wide two-phase (β + Z, α + Z, γ + Z) and narrow three-phase (α + β + Z, α + γ + Z) regions. The last two ones result from invariant four-phase peritectic and eutectic reactions, respectively. Coordinates of peritectic ( U 1 ) and eutectic ( E ) points were determined to be: U 1 – 1420 °C, ∼49Ti–4Si– 47Al; E – 1415 °C, 48Ti –4Si– 48Al. The solidus surface has its temperature maximum at 1545 °C corresponding to the invariant pseudobinary eutectic L↔β + Z with eutectic point at 65Ti – 8Si– 27Al. The isopleth at 10 at.% Si is given. The shape of the Ti 5 (Si,Al) 3 homogeneity range is discussed.