The dehydration kinetics of brucite were studied in situ by synchrotron X-ray powder diffraction (XRPD) in the temperature range 320–370 °C. The sequence of XRD spectra clearly reveals that the phase transformation of brucite into periclase occurs with increasing temperature up to 600 °C under ambient pressure. Our results show that there is a positive temperature dependence of the reaction rate k. Elevated temperatures will be conducive to the dehydration process. The obtained n values suggest that the reaction mechanism is a one-dimensional diffusion of the water molecules with an instantaneous nucleation. The influence of temperature on the reaction rate is well described by the Arrhenius equation, which yields an apparent activation energy Ea of 386 ± 12 kJ/mol and frequency factor A of 1.14 × 1029 s–1. The activation energy is influenced by factors such as grain size, shape, temperature, gas atmosphere, and surrounding water.