Polyaniline (PANI)-polyacrylic acid (PAA) composite thin films were deposited at room temperature on glass and polymethyl methacrylate substrates by introducing these into a freshly prepared chemical bath of HCl, PAA, aniline monomers and (NH4)(2)S2O8 Compared to the single PANI films, which were obtained from the same bath constitution but without PAA solution, the composite films showed a red shift at the maximum optical transmittance peak and a slightly lower electrical conductivity. Fourier transform infrared spectroscopy studies of the PANI composite thin films indicated the presence of the acid-base reaction product between PANI and PAA, as well as PAA molecule incorporation in the films. Atomic force microscopy analysis also showed morphologic and mechanical elasticity differences between the single PANI film the composite films deposited by the chemical bath method.