Rust converter is formed on rust carbon steel (corresponding to level A, B, C and D) in 5 types of denatured solutions basing on tannin having different components BTl, BT2, BT3, BT4 and BT5. Surface analysis methods SEM, EDX, IR, TGA... showed that the converter film had porous structure and relatively uniform on the surface. The results of measuring open circuit potential and potential polarisation of 5 kinds of converter films in NaCl3 percent solution showed that the converter film formed in BT3 and BT5 solutions had protection better than others and improve significantly the capacity adherence with the organic coatings.