Phase relations on the ternary system of Pb-Mo-Se at 1273 K were studied in the vicinity of Chevrel phase. PbMo6Se8. The PbMo6Se8 phase was found to be stabilized in the composition ranges, 0.9 less than or equal to x less than or equal to 1.1 and 7.50 less than or equal to (8 - y) less than or equal to 7.65 for the formula PbxMo6Se8-y. Superconducting transition temperature of this phase was observed at T-onset = 5.0 +/- 0.1 K. The tentative stability region of the CdMo6Se8 phase was observed to lie in the range 0.95 less than or equal to x less than or equal to 1.10 for CdxMo6Se7.5. Both phases showed the positive Seebeck coefficients of + 10- + 20 muV/K.