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Effects of excess Te on the thermoelectric properties of p-type 25% Bi2Te3-75% Sb2Te3 single crystal and hot-pressed sinter were characterized and understood with the micro-phase diagram near the stoichiometric composition obtained by measuring the equilibrium Seebeck coefficient. Thermoelectric properties of the 25% Bi2Te3-75% Sb2Te3 single crystal were varied with the amount of excess Te, as δ-phase of the single crystal becomes less Te-deficient with adding more excess Te. However, thermoelectric properties of the hot-pressed sinter were not varied with the amount of excess Te, because the composition of δ-phase is not changed with the amount of excess Te. While a maximum figure-of-merit of 2.39 × 10−3/K at 300 K was obtained for the 25% Bi2Te3-75% Sb2Te3 single crystal by adding 6 wt % excess Te, the hot-pressed 25% Bi2Te3-75% Sb2Te3 sinter exhibited the figure-of-merit of 2.97 × 10−3/K regardless of the excess Te amount.