Rare earth (RE) decreased the initial corrosion susceptibility of Zr-Ti deoxidized low alloy steel in a simulated marine environment through modifying the properties of inclusion and pearlite. The localized acidification caused by the dissolution of (RE)2O2S and (RE)xSy inclusions suppressed the hydrolysis of Ca2+ from the environment, inhibiting the deposition of CaCO3 and its participation in the formation of rust layer, which improved the rust layer compactness at first. This inhibition effect was diminished with time, while, the improved inner rust layer by RE effectively blocked the invasion of Cl-, promoting the enrichment of Cl- in the outer rust layer.