The precipitation of μ phase in a high W strengthening nickel-base superalloy and its effect on the tensile properties of the alloy were investigated at room temperature, 750 °C and 950 °C. The results indicate that the precipitation of μ phase firstly increases and then decreases with the increasing of temperature in the range from 850 °C to 1150 °C, with its peak around 1000 °C. The effect of μ phase on tensile properties of the alloy is related with temperature. It strengthens the alloy by impeding the motion of dislocations and increases the yield and ultimate strength at room temperature up to 750 °C, and slightly decreases the elongation. While μ phase deceases the yield and ultimate strength and increases the elongation of the alloy at 950 °C, because its precipitation consumes the solid (solution) strengthening element W which is the main strengthening form when the g￠ phase is largely dissolved.