The polyimide(PI) Langmuir-Blodgett(LB) ultra thin films were prepared by imidizing the PAAS LB films of PMDA and benzidine system with a thermal treatment at $250^{circ}C$ for 30min, where the PAAS LB films were formed on substrates by using LB technique. The thicknesses of one layer of PAAS and PI LB film that deposited at the surface pressure of 27mN/m were 20.9 and 4A, respectively. At low electric field, ohmic conduction($I^{propto}$ V) was observed and the calculated electrical conductivity was about $4.23{ imes}10^{-15}{sim}9.81{ imes}10^{-15}S/cm$. The dielectric constant of LB film was about 7.0.