Ethylene-octene copolymer(POE)samples exposed to γ—radiation under a series doses were investigated using solid state 13C-NMR．The chemical shifts of POE were assigned

and the peak evolution as a function of radiation dose was discussed．An obviously chain seission was found near the branch carbons

and the 13C—NMR spectra of the corresponding gels confirmed the result．Linewidths of irradiated POE samples of various absorbed doses were observed to which were related to the molecular mobility of the radiation-crosslinked polymer．