The aim is to explore the effects of time and temperature on the generation of free radicals in fingernails exposed to ionizing radiation by drying experiment, and to view the relationship between water content in fingernails of different individuals and the growth-rate of free radical concentrations through irradiation experiment. The free radicals concentrations was measured by electron paramagnetic resonance (EPR). The results showed that the more water content fingernails contained, the more free radicals sample would generate through the same absorbed dose. Meanwhile, as absorbed dose increased, the slope of fitting curve increased with the decreasing dispersion of the data measured from fitting curve. The slopes of fitting curve of samples irradiated at 1 Gy, 5 Gy, and 10 Gy were 0.8670, 1.7425 and 1.9628, respectively. The experimental results also showed that the difference of keratin content within fingernails would probably impact free radical concentration when fingernails were exposed to ionizing radiation. The current dosimetry method needs to be revised according to the difference of water content and keratin content among individuals. By solving individual difference, the more accurate dose reconstruction would be performed.Cited