Dual-curable composite resins of epoxymethacrylate/reduced graphene oxide (EMA/rGO) were prepared and applied as surface coating on a steel plate for improving corrosion resistance. To make EMA photo- and thermo-curable, diglycidyl ether of bisphenol-A was reacted with methacrylic acid at the same molar amounts through carboxyl-epoxide addition reaction. Analysis from gel permeation chromatography indicated that 65.4% of reaction products had a monomethacrylate-terminated structure having one terminal vinyl group for UV-cure and one epoxide group at the other end for thermo-cure. The epoxide conversion and structure of the produced EMA were further determined by NMR and FTIR analyses. Subsequently, rGO was added into the EMA resin along with curing agents and reactive diluent, and the resulting EMA/rGO mixtures were coated on steel plate and subjected to UV- and thermo-cure. The addition of rGO into the EMA coating increased the surface hydrophobicity and also the pencil hardness to 5H. The results of potentiodynamic polarization revealed that the addition of only 2−phr rGO into the EMA coating could reduce the corrosion rate of the steel by 60% when compared to the pristine EMA-coated steel. Such EMA/rGO composite resins can be useful for coating and painting industries.