The work aims to improve the thermal stability and hardness of Ni based coating. Ni-Mo coatings with different Mo content were prepared on the surface of brass substrate by direct current electrodeposition under acid condition. The influences of different concentrations of sodium molybdate dihydrate (20, 40, 60 g/L) and different annealing treatment (300, 400, 500 ℃) on the microstructure and hardness of Ni-Mo coating were investigated. The microstructure and properties of the coatings were characterized by XRD, SEM, EDS and nano-indentation tester. With the increment of the contents of sodium molybdate, the contents of Mo in the coating increased gradually and the grain size was refined with the reduction of crystallinity. Upon post annealing at elevated temperature, the grain sizes of Ni-Mo coatings were coarsened and the phases were transformed from amorphous to crystalline. Meanwhile, the XRD results showed that Mo elements were dissolved in Ni matrix in the form of Ni (Mo) solid solution, presenting solution strengthening in the coatings with the increment of Mo contents. In addition, the hardness of the coating was reduced with the increase of annealing temperature, while hardness of the coating was enhanced first and then dropped at higher Mo contents. However, the hardness of the coating in both situations was far higher than that of the copper matrix. Compared with as-deposited samples, the hardness of Ni-Mo coatings changed slightly upon annealing at 300 ℃, and reduced significantly at 500 ℃. Thus, it is concluded that the addition of Mo can improve the thermal stability and mechanical properties of Ni-based coatings.