The influence of pre-strain on the formation of bimodal grain structures and tensile properties of a Co-20Cr-15W-10Ni alloy was investigated.The bimodal grain structures consist of fine grains(FGs;2-3 μm in diameter)and coarse grains(CGs;8-16 μm in diameter),which can be manipulated by changing the pre-strain(ε=0.3-0.7)and annealing temperatures(1000-1100℃).High pre-strain applied in the samples can intensify the plasticity heterogeneity through increasing the total dislo-cation density and the local volumes of high-density dis-locations.This can essentially result in finer FGs,a higher FG volume fraction,and overall grain refinement in the samples after annealing.High-temperature essentially increases both the size and volume fraction of CGs,leading to an increase in the average grain size.The tensile test suggests that the bimodal grain structured samples exhib-ited both high strength and ductility,yield strengths of 621-877 MPa and ultimate tensile strengths of 1187-1367 MPa with uniform elongations of 55.0％-71.4％.The superior strength-ductility combination of the samples arises from the specific deformation mechanisms of the bimodal grain structures.The tensile properties strongly depend on the size ratio and volume fraction of FGs/CGs in addition to the average grain size in the bimodal grain structures.The grain structures can be modified via changing the pre-strain and annealing temperature.