A new thermomechanical processing named the martensite process which can easily fabricate the ultrafine grained steels without severe plastic deformation was developed. In this process, martensite is used as the starting structure. The martensite starting structure was conventionally cold-rolled by various reductions and then annealed at various temperatures. The cold-rolled martensite mainly exhibited lamellar structure, which is typical in severely deformed materials. The area fraction of the lamellar structure increased and the mean spacing of the lamellar boundaries decreased with increasing the rolling reduction, accompanying significant strengthening. After subsequent annealing at warm temperatures, the lamellar structure turned to equiaxed ultrafine ferrite grains with carbides precipitated uniformly, and at higher temperatures conventional recrystallization occurred to form coarse grained structure. The recrystallization temperature became lower with increasing the rolling reduction. The specimen rolled to intermediate reduction (50%) performed the largest ductility keeping high strength around 900MPa after warm-temperature annealing.