In-situ preparation method of self-assembled polyaniline (PANI)/ poly(styrene sulfonic acid) (PSS) composite ultra thin films on aminosilane grafted surfaces was proposed. PSS was adsorbed onto the aminosilane grafted Si-wafers, then PANI/ PSS composite ultra thin films were prepared in-situ by template polymerization utilizing ionic interaction between PSS and aniline. PANI/ PSS composite ultra thin films were characterized by time of flight secondary ion mass spectroscopy (TOF-SIMS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible-near infrared (UV-Vis-near IR) spectroscopy. Composition of PANI/ PSS composite ultra thin films estimated by XPS gave good agreement with the calculated value based on the chemical structures. AFM images and UV-Vis-near IR spectra revealed that the progress of conjugation of PANI/ PSS composite ultra thin films. From these results, it can be inferred that the formation of ultra thin films is closely related to the electrostatic character of functionalized substrate surfaces. In this method, PSS plays an important role as a template for polymerization of aniline. Therefore, the positively charged surfaces facilitated the formation.