Electron spin resonance (ESR) spectroscopy was used to investigate the effect of irradiation dose on the ESR signal intensity of irradiated crabs and the stability of these radicals under 9 weeks of storage. Swimming and small crabs were irradiated with doses of 0, 1, 2, 3, 5 and 7 kGy using a Co-60 irradiator at ambient temperature. A claw, a walking leg and a carapace of the crab pieced and dried were placed in a resonant quart tube within an EPR X-band spectrometer. The irradiated crabs presented an asymmetric absorption in shape at g₁=2.002±0.003 and g₂=1.998±0.005, and were different fro the non-irradiated ones. The intensity of the ESR signals was greatest in the claw, intermediate in the carapace and lowest in the walking leg. Samples given low and high doses of irradiation could also be distinguished. The ESR signal after irradiation was stable, even after a 9-week storage.