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The superconducting transition temperature of single unit cell FeSe on SrTiO₃ (STO) heterostructure is known to be significantly enhanced over that of bulk FeSe, presumably due to a combination of the electron charge transfer from the STO substrate to FeSe and an enhanced electron-phonon interaction across the heterointerface. Here, we explored the possibility of similar physics in monolayer NbSe₂ on n-type and p-type graphene substrates and found that the transition temperature is much higher in the latter heterostructures than in the former ones. The enhancement of superconductivity in monolayer NbSe₂ on p-type graphene is likely a result of the charge transfer effect. We also studied the temperature dependence of the resistance of NbSe₂ under an in-plane magnetic field. The extracted in-plane upper critical field of monolayer NbSe₂ overcomes the Pauli paramagnetic limit, suggesting Ising pairing property. We will talk about the properties of monolayer NbSe₂ films grown on other oxide substrates.