A new Ni-based superalloy with the refined grains is to be used in industrial and aircraft turbines because of its high strength and excellent fatigue resistance at lower and medium temperatures (500~800 ℃). The grains with six different sizes have been made by decreasing the pouring temperature from 1460 to 1480 ℃ then 1500 ℃ and adding refiner to alloy and planting seed on the surface of mold. The size of equiaxed crystal grain is reduced to 0.5 mm in the center part of specimen with the columnar crystals in the outside of specimen made by the refining process which is finer than those of traditional process. It has been found that γ' phase and carbide are finer in refined grains than those in the coarse grains made by decreasing the pouring temperature. The room-temperature tensile properties and high cycle fatigue properties of tested alloy are improved with decreasing grain size. The stress-rupture properties are increased under the conditions of 760 ℃ and 662 MPa while are decreased with decreasing the grain size. The grain structure and size are refined by the refining process that dominated the excellent mechanical properties of tested alloy at lower and medium temperatures. However, it is not good for the mechanical properties at high temperatures.