The Ultrafine-grained CoCrFeMnNiGd_0.15 high-entropy alloy (HEA) was prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructure and mechanical properties of CoCrFeMnNi Gd_0.15 high-entropy alloy was investigated. It was found that the sintered CoCrFeMnNiGd_0.15 alloy showed a multi-phase microstructure including the FCC matrix, a rare earth oxide (Gd₂O₃) and a tetragonal phase rich in Gd, Ni and Mn element. As the sintering temperature increased, the content and size of the precipitated phase increased continuously, the compressive yield strength of the alloy decreased while the plasticity showed the opposite trend. The sintered alloy achieved the best comprehensive mechanical properties at the sintering temperature of 900 °C, with a compressive yield strength of 1662 MPa, compressive strength of 2518 MPa, plastic strain of 30.6% and Vickers hardness of 458 Hv. With the increase of temperature, the fracture morphology of compressive specimens consisted of fine equiaxed dimples, the diameter and depth of the dimples increased continuously and some tearing ridges were observed.