The microstructure and corrosion behavior of weathering steel in three solutions (S1: 3.5 wt.% NaCl, S2: 3.5 wt.% NaCl+0.052 wt.% NaHSO₃, S3: 3.5 wt.% NaCl+0.907 wt.% NaHCO₃) were investigated. A high proportion of random boundaries is responsible for strong corrosion sensitivity. The thickness of rust increases with immersion time and is in the order of S1>S3>S2. The rust formed in S1 and S2 solutions mainly consists of γ-FeOOH phase, but the latter is less protective. The rust formed in S1 solution is dense and thick resulting in its protection being similar to that in S3 solution.