Abstract: To investigate the corrosion resistance of high-heat-input welded joints of 60 mm-thick EH36 and EH40 shipbuilding steels in marine environments, three types of joints, namely EH36 joints welded with imported flux-cored wire, EH36 joints welded with domestic flux-cored wire, and EH40 joints welded with imported flux-cored wire, were selected. Potentiodynamic polarization and electrochemical impedance spectroscopy were employed to evaluate their electrochemical corrosion behavior in 3.5% NaCl solution. Optical microscopy and scanning electron microscopy were used to characterize the microstructures of the joints, and the microstructure-related mechanism affecting corrosion resistance was discussed. The results show that the corrosion resistance of the weld zones follows the order of EH36 imported > EH36 domestic > EH40 imported. The EH36 joint welded with imported wire exhibits the lowest corrosion current density of 6.9024 μA·cm^-2 and the highest polarization resistance of 3525.7 Ω·cm², indicating the best corrosion resistance. The EH36 joint welded with domestic wire shows the most positive corrosion potential of -0.396 V, but its overall corrosion kinetic performance is slightly inferior to that of the imported EH36 joint. The EH40 joint welded with imported wire presents the highest corrosion current density and the lowest corrosion resistance. Microstructural analysis indicates that the EH36 imported joint possesses relatively fine and uniform grains in the heat-affected zone, densely interwoven acicular ferrite in the weld zone, finely dispersed inclusions, and better microstructural compatibility among the weld metal, heat-affected zone and base metal. In contrast, the EH36 domestic joint shows local coarse grains, larger inclusions and non-uniform microstructure, while the EH40 imported joint, despite its good weld formation, exhibits poorer microstructural uniformity and acicular ferrite distribution than the EH36 imported joint. The results demonstrate that grain refinement, inclusion dispersion and effective acicular ferrite formation are the key microstructural factors for improving the corrosion resistance of high-heat-input welded joints of shipbuilding steels.