This thesis studies the corrosion inhibition effect of lignin from different biomass sources on mild steel in chloride-containing solutions. Eight lignin samples were investigated: Beer, Canapa, Colza, LL05 (from sunflower seeds), LL13 (from grape seeds), Protobind, White Rice, and Yellow Rice. The samples were added directly to sodium chloride solutions and tested as solution-phase inhibitors. The main purpose was to compare their corrosion behavior and to understand whether the origin and chemical structure of lignin can influence its protective effect on mild steel. The experiments were carried out in 0.6 M NaCl and 0.1 M NaCl. The corrosion response was evaluated by Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization, and Tafel analysis.