A chemically cross-linked and water-swollen poly(3-thiopheneacetic acid) (P3TAA) gel was synthesized, and its swelling and spectral changes associated with its ionization were studied. The gel undergoes an abrupt red shift in the electronic spectra at a certain pH, suggesting that a conformational transition due to ionization occurred despite the chemical cross-linkage. By changing the solvent composition, during cross-linking, gels with an enhanced pi conjugated structure were prepared. By doping of P3TAA gel with a HClO4 solution, a satisfactorily high electrical conductivity was obtained.