The passivation and corrosion of metal are significantly affected by its surface state and chemical characteristics. In practical engineering, the reinforcement is with mill scale or rust stains. Its passivation and corrosion are obviously different from the descaled one. This book briefly discusses the pseudo-passivation behavior and corrosion mechanisms of hot-rolled rebars with mill scale and provides the corresponding protection measures, which can be used as a reference for corrosion or civil engineers.