Abstract: To improve the properties of reduced activation alloy (CLF-1) at high temperature, the oxide dispersion strengthened (ODS) CLF-1 was prepared by ball-milling and hot isostatic pressing mixed powders of Ar atomized CLF-1 and nanometer Y₂O₃. The samples were treated at different temperatures for different time, and the microstructure was analyzed and mechanical performs were measured. The result shows that the main matrix is tempered martensite after normalizing and tempering, and the grain size is quite uniform after normalizing at 1 100 ℃. The microstructure is less affected by the tempering temperature, while the Vickers hardness is reduced when tempering temperature is escalated. In the heat treatment sample, the dispersed particles of Y₂O₃ and piling up of dislocation are observed, which demonstrates the dispersion strengthened effect. Larger particles with diameter of about 100 nm are inclined to distribute at the grain boundaries, while smaller ones scattering within the grains. The ODS CLF-1 in present study displays excellent tensile properties at high temperature, the tensile strength is up to 370 MPa, and the elongation is 18.5% at 600 ℃. The tensile yield strength and ultimate tensile stress decrease with the increase of temperature.