Abstract: By power metallurgy method, the samples of ODS-HT9 steel, which were strengthened by dispersion oxide of 0.1%~0.9% Y₂O₃, were prepared in order to study the effect of nano-Y₂O₃ on the microstructure and mechanical properties of HT9 steel. The HV, tensile strength, and elongation of the samples were measured. The distribution, the shape, and the phase structure of Nano-Y₂O₃ oxide particles in the sample were observed by transmission electron microscope (TEM), and the fracture microscope was by scanning electron(SEM). The results show that Y₂O₃ particles were homogenously distributed on the HT9 steel, and their shape and phase structure have no change after ball milling and hot-pressing. Due to the strengthened dispersion of nano-Y₂O₃ particles, the tensile strength and Vickers hardness of ODS-HT9 steel increase, and the elongation decreases, significantly, with the increasing of Y₂O₃ addition. If the addition of Y₂O₃ is less than 0.7%, the fracture of samples is ductile. But, if the addition of Y₂O₃ increases furthermore, the fracture will change to brittle. The ODS-HT9 steel samples with 0.3%~0.5%(mass fraction) of Y₂O₃ have a better properties. The tensile strength and elongation reach to 913~936 MPa and 10.7%~11.2%, respectively. The results will be helpful to the study of ODS-HT9 high temperature performance and its practical application in reactors.