4,4′-Bis(chloroacetyl)diphenylether was synthesized and its polycrystal form was produced. This polycrystal sample was irradiated by gamma rays (60Co) for 72 h. The ESR method was used to observe formation of free radical on the sample. ESR signal was not recorded from the non-irradiated sample, but the irradiated polycrystal sample exhibited complex ESR spectra. The measurements were carried out in the temperature range of 120-450 K. It was observed that the shape of the spectrum was dependent on the temperature. Two identical radicals were determined on the irradiated sample. Respectively, the spin density, hyperfine, and g values were found to be ρHa=0.53, ρHb=0.23,aCl=1.263mT,aHa=1.486mT, aHb=0.637mT, and g1 = 2.0115 for the Radical I; ρHx=0.22,ρHy=0.14,aCl=0.905mT, aHx=0.615mT,aHy=0.391mT, and g2 = 2.0383 for the Radical II. © 2013 Elsevier B.V. All rights reserved.