Objective To explore the feasibility of EPR in vivo fingernail dosimetry to address the difficulty in separating mechanically induced signals from fingernail EPR dosimetry for need of nuclear medical emergency aid.Methods Using the specially designed EPR in vivo measurement system,uncut fingernails were measured to obtain the characteristics of EPR signal without mechanically induced signals.The in vivo fingernail experiment was carried out to evaluate the impact of in vivo condition on the spectra.Actual in vivo measurement experiment was conducted to evaluate the interference of the in vivo condition on EPR spectra.Results The background signal distribution of uncut fingernails was obtained and background signals had no significant difference between male and female(P＞0.05).The dose response curve in the range of 2-10 Gy was established,and the half-life of the fingernail radiation-induced signal was approximately 5 d.The water treatment combined with temperature-changing was established for restoring the background signal.EPR signal obtained after restoring treatment has no significant difference with background signal (P＞ 0.05).The EPR spectra of in vivo fingernails were obtained.Conclusions The EPR spectra without mechanically induced signals can be acquired by this method.The feasibility of the in vivo fingernail EPR dosimetry is preliminarily verified.