Indole-5-carboxylic acid is an indole derivative. On electropolymerization, it affords electroactive polymer film of poly(indole-5-carboxylic-acid). Different concentrations of indole-5-carboxylic acid in sulfuric acid solution has been investigated for the preventive action against mild steel corrosion. On electropolymerization it affords a trimeric product. Characterization studies of the trimeric product by 1H NMR and various one- and two-dimensional NMR techniques have been reported.