Phase equilibria of the Ni-Co-Sn ternary system at 700 °C and 1000 °C were experimentally determined by using electron probe microanalyzer and X-ray diffraction. No ternary compound was found at 700 °C and 1000 °C. There was an extensive region of mutual solubility existing between βCo3Sn2 phase and Ni3Sn2(h) phase. Three Ni-Sn binary compounds [Ni3Sn(l), Ni3Sn(h) and Ni3Sn4] showed absolutely different solubilities for the element Co. The maximum solubility of Co in Ni3Sn(l) and Ni3Sn4 phases at 700°C were 6.9 at.% and 25.6 at.%, and the solubility of Ni3Sn(h) phases changed into 15.5 at.% at 1000°C. The Ni-Co side presented an interconnected (αCo, Ni) phase region at both 700oC and 1000°C and its homogeneity range for Sn was from 1 at.% to 10.5 at.%. The solubility of Ni in the linear compound CoSn phase was about 15.9 at.%.