Polyimide is a well-known organic dielectric material, which has not only high chemical and thermal stability but also good electrical insulating and mechanical properties. In this research, the electric conduction mechanism of PI Ultra-Thin Films was investigated at room temperature. At low electric field, ohmic conduction $(I{propto}V)$ was observed and the calculated electrical conductivity was about $4.23{ imes}10^{-15}{sim}9.81{ imes}10^{-15};S/cm$. At high electric field, nonohmic conduction $(I{propto}V^2)$ was observed and the conduction mechanism was explained by space charge limited region effect. The dielectric constant of PI Ultra-Thin Films was about 7.0.