Stable monolayer of the polyaniline(PAn) doped with dodecyl benzenesulfonic acid(DBSA) can form on the pure water surface. Pie multilayer ultrathin film can be successfully deposited by Langmuir-Blodgett(LB) technique onto CaF2 substrate. The limiting mean molecular area and collapse pressure observed are 0.066 nm(2) and 35 mN m(-1) respectively. The multilayer LB film and casting film were all characterized by IR and UV-Vis-NTR spectroscopies.