After X-rays or γ-ray irradiation, fingernails as biomaterial having good radiosensitivity, would generate free radicals. Electron paramagnetic resonance (EPR), a tool which can qualitatively and quantitatively measure free radicals, has been used to detect the radical concentration induced by irradiation so that estimate irradiated dose of victims and conduct triage. As an immature dosimetry method, it still has many problems, and some researchers are unfamiliar with quantitative utilization of electron paramagnetic resonance. Therefore, the theory, matters needing attention and recent progress of fingernail electron paramagnetic resonance quantitative measurements will be reviewed.Cited