Single crystals of dimethyl-1,3-cyclohexanedione (C8H12O2) were produced by slow evaporation of the concentrated ethyl acetate solutions. These single crystals were exposed to 60Co γ -rays with a dose speed of 0.950 kGy/h at room temperature for 24, 48, and 72 h. The free radicals of the samples irradiated for 48 and 72 h were detected using electron paramagnetic resonance (EPR)-X-band spectrometer. EPR measurements were performed between 120 and 300 K. The sample irradiated for 48 h by γ -rays was rotated in steps of 10° at 298 K. The spectrum parameters were found to be dependent on the temperature. Two radicals were determined in the molecular structure irradiated. These radiation damage centers were called R1 and R2. The average values of g and the hyperfine coupling constants were calculated as follows: a Ha=6.84 G, a Hb=3.60 G, g=2.0040 for R1, a H=28 G, g=2.0062 for R2.