The surface modification of Kapton film by means of plasma polymer deposition is discussed from the viewpoint of improving the adhesion between copper metal and Kapton film substrate. Plasma polymers of AN (acrylonitrile) and FN (fumaronitrile) were used for the surface modification, and the adhesion between the copper metal and the plasma polymer-coated Kapton film was evaluated by the T-peel strength measurement. The surfaces of peeled layers were analyzed by X-ray photoelectron spectroscopy (XPS) and the failure mode is discussed. The plasma polymer deposition of AN and FN shows an effective improvement in the adhesion between the copper metal and Kapton film; in particular, the AN plasma polymer deposition increased the peel strength 4.3 times. Failure occurred mainly in the Kapton film, and the adhesion between the AN plasma polymer and the Kapton film and that between the copper metal and the AN plasma polymer were found to be quite strong.