Abstract. We report a half-life of the ground state of 184 Re populated by the 185 Re(γ,n) 184 Re reaction with the Laser Compton scattering γ-rays generated through relativistic engineering. The γ rays are provided at the electron storage ring NewSUBARU. The half-life of the 3 − ground state of 184 Re, 38.0±0.5 d, has been taken as a recommended value, which was measured using deuteron-induced reactions. However, this half-life may include a possible contribution from the 8 + isomer (T 1/2 = 169±8 d) of 184 Re since the presence of the isomer was not known at that time. In contrast, the (γ,n) reaction has the advantage to selectively populate the ground state because this reaction does not bring large angular momentum. The measured half-life of 35.4 ± 0.7 d is shorter than the previous half-life by about 7%. This difference is crucial for applications using the activation method.