Five partial isothermal sections of the Ti–Al–Si system up to 70 at% Al and 40 at% Si have been determined experimentally between 800 and 1200 °C. Seven alloys were heat-treated for 24–1504 h and characterized utilizing scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential thermal analysis. No ternary phase was found and αTi, βTi, Ti3Al, TiAl, TiAl(1d-APS), TiAl2, TiAl3 are in equilibrium with Ti5Si3. A partial vertical section at 9 at% Si shows that all determined data are consistent with each other.