An in situ and ex situ reinforced powder metallurgy(PM) steel was prepared by the combination of high-energy ball milling and subsequent hot pressing of elemental mixed powders of Fe–10Cr–1Cu–1Ni–1Mo–2C by mass with the addition of Nb C particles. A 40-h milling pretreatment makes the powder particles nearly equiaxed with an average diameter of ~8 μm, and the ferrite grain size is refined to ~6 nm. The sintered density reaches 99.0%–99.7% of the theoretical value when the sintering is conducted at temperatures greater than 1000°C for 30 min. In the sintered bulk specimens, the formation of an in situ M7C3(M = Cr, Fe, Mo) phase is confirmed. M7C3 carbides with several hundred nanometers in size are uniformly distributed in the matrix. Some ultra-fine second phases of 50–200 nm form around the ex situ Nb C and in situ M7C3 particles. The sintered steel exhibits an excellent combination of hardness(> Hv 500) and compressive strength(2100–2420 MPa). An in situ and ex situ reinforced powder metallurgy (PM) steel was prepared by the combination of high-energy ball milling and subsequent hot pressing of elemental mixed powders of Fe-10Cr-1Cu-1Ni-1Mo-2C by mass with the addition of Nb C particles. A 40-h milling pretreatment makes the powder particles nearly equiaxed with an average diameter of ~8 μm, and the ferrite grain sizes are refined to ~ 6 nm. The sintered density reaches 99.0% -99.7% of the theoretical value when the sintering is conducted at temperatures greater than 1000 ° C for 30 min. In the sintered bulk specimens, the formation of an in situ M7C3 (M = Cr, Fe, Mo) phase is identified. M7C3 carbides with several hundred nanometers in size Some uniformly distributed in the matrix. Some ultra-fine second phases of 50-200 nm form around the ex situ Nb C and in situ M7C3 particles. The sintered steel exhibits an excellent combination of hardness (> Hv 500) and compressive strength (2100 -2420 MPa).