The phase equilibria in the Ni-Al-Sn ternary system were investigated by means of electron probe microanalysis and X-ray diffraction. The experimental results showed that: (1) No ternary compound was found at 800°C and 1000°C. (2) The Ni-Al side presented four binary compounds included NiAl, Ni3Al, Al3Ni and Al3Ni2 phases. The solubilities of Sn in the binary NiAl and Ni3Al phases were determined as 3.1 at.% (Atomic ratio) and 14.7 at.% at 800°C, and 3.0 at.% and 8.0 at.% at 1000°C, respectively. As for the binary Al3Ni and Al3Ni2 phases, the solubilities of Sn were almost negligible. (3) The Ni-Sn side displayed three binary compounds included Ni3Sn(r), Ni3Sn(h) and Ni3Sn2(h). The Ni3Sn(r) phase was stable at 800°C dissolving 4.2 at.% Al but it was replaced by the Ni3Sn(h) phase with a 5.5 at.% Al solubility at 1000°C. The solid solubility of Al in Ni3Sn2(h) was 8.4 at.% and 12.1 at.% at 800°C and 1000°C respectively. (4) The Al-Sn side was occupied by an interconnected liquid region having only ~1 at.% Ni solubility.