A bulk d0 NaN of rocksalt or zinc-blende structure was predicted to be a ferromagnetic half metal and furthermore the half-metallicity would be retained in thin films. Such half metallicity of d0 ferromagnetic NaN is attractive for possible application in a spintronics device, such as a spin transfer torque magnetic random access memory. In this study, we carried out first-principles calculations on magnetocrystalline anisotropy rocksalt structured NaN thin films with different thicknesses, using Vienna Ab-initio Simulation Package code. It was found that the NaN(001) thin films have perpendicular magnetization with quite low magnetocrystalline anisotropy energies of order of 10 µeV, but capping of a 5d-transition metal Ta monolayer over the NaN(001) thin films enhances the perpendicular magnetocrystalline anisotropy energies significantly, more than 10 times. Furthermore, the 1 (Ta)/NaN(001) systems retain their half-metallicity except the NaN layer just below Ta.