The low-temperature radiolysis of poly(butylene terephthalate), poly(ethylene terephthalate), and diethyl terephthalate was studied by electron spin resonance spectroscopy. The radiation-induced formation of radicals of the cyclohexadienyl type was observed for all the samples studied. It was shown that the radicals of the cyclohexadienyl type represented a considerable fraction of neutral radicals produced in the radiolysis of phthalates under consideration. The identification of the signals of various alkyl-type radicals is discussed. The kinetics of radical decay at room temperature was investigated.