The corrosion resistance properties of epoxy coatings applied to St37 carbon steel were modified with polysulfide and nano cerium oxide (CeO2). The surface chemistry of the epoxy/polysulfide coating was studied by Fourier transform infrared spectroscopy, which confirmed the presence of the thiol group. The toughness and corrosion properties of epoxy/polysulfide composites were investigated by cupping and electrochemical impedance spectroscopy (EIS) tests, respectively. Results showed that the addition of 10 wt% of polysulfide to epoxy, led to a notable increase in toughness and corrosion resistance. Epoxy/polysulfide/CeO2 nanocomposites were prepared by incorporating 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, and 6 wt% of CeO2 nanoparticles into the epoxy coating with 10 wt% of polysulfide. Field emission scanning electron microscopy observations indicated the uniform dispersion of 1 wt% nano CeO2 and agglomeration of higher concentrations of particles in the composite. The effect of nano CeO2 on the corrosion behavior of the coatings was investigated in a 3.5% NaCl solution using EIS and salt spray tests. The adhesion strength of the nanocomposites was measured by a pull-off adhesion tester. Results revealed that the incorporation of 1 wt% CeO2 nanoparticles significantly increased the corrosion resistance and adhesion strength of the epoxy/polysulfide coatings.