Abstract: The corrosion behaviors of four low-alloy steels welded joints have been studied by indoor exposure tests and electrochemical tests and the composition, inclusions and microstructures of such joints were also researched, For the different joints, the corrosion resistance of the parent-metal and heat-affect-zone is mainly dependent on the compositions of the steels; while the corrosion resistance of the welded bonds and welded metal is mainly dependent on inclusions and microstrures. For three distinct zones of the same welded joint, the corrosion resistance is different from each other. The corrosion resistance of distinct zones for the same welded joint is closely related to the chemical compositions, inclusions and microstructures of the distinct zones respectively.