The feasibility of an optical fibre corrosion sensor (OFCS) was studied. A multi-mode fibre was metallised by physical vacuum deposition and electroplating of a Fe–C alloy film on a 1–2cm uncladded section of an optical fibre. The shift of light power transmitted through the fibre was registered with corrosion. Microanalysis was carried out to show the formation of metallised film. The electrochemical process of the corrosion on the fibre was researched by continuously monitoring open potential E corr , linear polarized resistance R p and electrochemical impedance spectra.