Tetrafluoroethylene-hexafluoropropylene (FEP) copolymer sheets were modified by remote H-2, N-2, O-2, and Ar plasmas, and the effects of the modification on adhesion between FEP sheets and copper metal were investigated. The four plasmas were able to modify the FEP surfaces' hydrophilicity. Defluorination and oxidation reactions on the FEP surfaces occurred with exposure to the plasma. The hydrophilic modification by H-2 plasma was best, followed by modification by O-2, Ar, and N-2 plasmas. The surface modification of FEP by all four remote plasmas was effective in improving adhesion with copper metal. The peel strength order of the FEP/Cu adhesive joints was H-2 plasma > Ar plasma > N-2 plasma > O-2 plasma. Mild surface modification is important for the adhesion improvement of FEP with Cu metal.