Transformable 9Cr oxide dispersion strengthened (ODS) steel was prepared by mechanical milling and consolidated by spark plasma sintering (SPS). Microstructural features in different fabrication stages were studied by X-ray diffraction, optical microscopy, scanning and transmission electron microscopy. In the mechanical milling stage, deformed, amorphous and fractured Y2O3 particles are identified, and certain amount of Y2O3 may decompose into the matrix. As a rapid densification technique, SPS will retain the high density of dislocations produced in milling. For both as-sintered and as-annealed 9Cr-ODS steels, interface structures and orientation relationships between Y2O3 and the iron matrix have been examined, as well as the size distributions of Y2O3 particles. The as-sintered 9Cr-ODS steel exhibits higher strength at room temperature than the as-annealed one, and contributions of various microstructural features to yield strength of 9Cr-ODS steels in both conditions have been evaluated.