The effects of $N^+$ ion implantation on surface structures andproperties of polyimide films were investigated. The polyimide films were modified by 100keV ionsusinga $N^+$ source at flow rates ranging from $5{ imes}10^{14}$ to $5{ imes}10^{17}$ ions/$cm^2$ with an ion current density of 10 ${mu}A/cm^{2}$. After the ion treatment, the chemical structures and morphology of the surfaces were examined in detail by X-ray photoelectron spectroscopy and scanning probemicroscopy, respectively. The implantation of $N^+$ ions not only destroyed the chemical bonds as a result of random collisions by the incident ions and the energy transfer to the polymeratoms but also roughened the surface of the polyimide film. The roughness of thepolyimide surface increased with increasing ion fluence, and the contact angle of the polyimide surface with water decreased.