To develop medium Mn steel (MMS) matrix composites reinforced by AI2O3 particles, the effect of Nb on the interfacial wettability of AI2O3/MMS and its mechanism were investigated in this paper. The results show that the wetting angle of the specimens with different Nb contents are bigger than that of the specimen without Nb at the first stage, and then decreases with time at 1450℃. At certain time, the wetting angle is lower than that of the specimen without Nb. At 1550 and 1600℃, the wetting angle of the specimens containing Nb decreases quickly with time at first stage. After 10 min, the wetting angle reaches a steady state, and hardly changes with time. The mechanisms of Nb to improve the wettability can be attributed to the enrichment of Nb at the interface and Nb serves as surface active agent of MMS at T<1550℃, and as catalyzer for the interfacial reaction of AI2O3/MMS at T>1550℃, and reduces the interfacial energies. To develop medium Mn steel (MMS) matrix composites reinforced by AI2O3 particles, the effect of Nb on the interfacial wettability of AI2O3 / MMS and its mechanism were investigated in this paper. The results show that the wetting angle of the specimens with different Nb contents at larger time than that of Nb at the first stage, and then decreases with time at 1450 ° C. At certain time, the wetting angle is lower than that of the specimen without Nb. At 1550 and 1600 ° C, the wetting angle of the tests containing Nb minimization with time at first stage. After 10 min, the wetting angle reaches a steady state, and hardly changes with time. The mechanisms of Nb to improve the wettability can be attributed to the enrichment of Nb at the interface and Nb serves as surface active agent of MMS at T <1550 ° C, and as catalyzer for the interfacial reaction of AI2O3 / MMS at T> 1550 ° C, and reduces the interfacial energies.