Polyaniline (PANI) doped with hydrochloric acid (HCl), sulpharic acid (H2SO4) and formic acid (HCOOH) was synthesized by a chemical oxidative polymerization technique. The oxidizing agent used for this method is potassium dichromate. The polymer products were characterized by FTIR and UV-visible spectroscopy. The FTIR results showed that the doping degree of PANI-HCOOH is the greatest one. A successful doping of HCOOH in PANI was observed in UV-visible spectroscopy. Three steps decomposition observed from the thermo gravimetric analysis (TGA).