The metallic matrix composite with ceramic nano-particles has a wide prospect in many applications due to its superior properties. The nanocomposite Ni-WC coating has been synthesized by using DC co-electrodeposition of Ni with WC nano-particles. Its hardness was measured by using ultra-micro hardness tester. Its corrosion and passive properties were investigated in 0.05 mol/L H₃BO₃+0.075 mol/L Na₂B₄O₇ buffer solution with pH=9.0 by using potentiodynamic polarization measurement. As compared to pure nanocrystalline (nc) Ni, nanocomposite refined remarkably, with average grain size about 21 nm and the hardness increase of 80%, reaching about 651 HV. The corrosion current density i_corr is 1.29×10^-7 A/cm²,approximately one magnitude order lower than that of nc Ni. With the similar passive film breakdown potential, nanocomposite exhibits a lower passivation potential E_p of 10 mV and a much lower passive current density i_p of1.79×10^-6 A/cm², about 1/7 that for nc Ni. According to the Mott-Schottky analysis together with point defect model, the passive film on the nanocomposite exhibits p-type semi-conducting behavior,similar to that on the nc Ni. The grain refinement of Ni is beneficial to the reduction of both the donor density and diffusion coefficient.