The layer-by-layer self-assembly of polyaniline (PAN) and polyacrylic acid (PAA) has been accomplished via the alternate spontaneous adsorption of base-type PAN from its dilute N-methylpyrrolidinone solution and PAA from its aqueous solution based on the acid-base reaction of PAN and PAA. The thickness of the films can be manipulated at nanometer scale by the concentration of PAN solution and recycling times. It is found that the PAN base film cannot be doped to emeraldine salt by PAA in the presence of ammonium persulfate. The UV-Vis spectroscopy was used to characterize the self-assembling process and the oxidation states of PAN. The electrochemical cyclic voltammetric and electrochromic properties of the self-assembled films were also studied.