The hot deformation behaviors of a 9Cr oxide dispersion-strengthened (9Cr-ODS) steel fabricated by mechanical alloying and hot isostatic pressing (HIP) were investigated. Hot compression deformation experiments were conducted on a Gleeble 3500 simulator in a temperature range of 950–1100°C and strain rate range of 0.001–1 s−1. The constitutive equation that can accurately describe the relationship between the rheological stress and the strain rate of the 9Cr-ODS steel was established, and the deformation activation energy was calculated as 780.817 kJ/mol according to the data obtained. The processing maps of 9Cr-ODS in the strain range of 0.1–0.6 were also developed. The results show that the region with high power dissipation efficiency corresponds to a completely recrystallized structure. The optimal processing conditions were determined as a temperature range of 1000–1050°C with strain rate between 0.003 and 0.01 s−1.