The transitions of copolymer of tetrafluoroethylene-hexafluoropropylene (FEP) were studied by using the dynamic mechanical and dielectric relaxatiOn methods．Three mechanical transition peaks i.e．a.β and γ，were observed over a temperature range from一90℃ to 160℃ for FEP eop olymer．Efleets of HFP content on the transitions were discussed． Similar to mechanical relaxation．there are three transi．tion peaks of a-γ and δ existing between —186 and 150℃ by dielectric method．Ex-perimental data showed that the peaks measured by dynamic mechanical method are consistent with the peaks measured by dielectric method．The meehanism of dielee-tric δ transition is explained in detail．