Eu2+-doped magnesium haloborate Mg3B7O13Cl was synthesized by the conventional high-temperature solid-state reaction. The phase formation was confirmed by X-ray powder diffraction (XRD) measurements and structure refinement. The photoluminescence excitation and emission spectra, and decay curves were measured. Under the excitation of near-UV light, Eu2+-doped Mg3B7O13Cl presents a narrow blue-emitting band centered at 423nm. The maximum absolute quantum efficiency (QE) of Mg3B7O13Cl:Eu2+ phosphor was measured to be 80% excited at 385nm light at 300K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects. Moreover, Mg3B7O13Cl:Eu2+ phosphor shows scintillation characteristics excited by X-ray irradiation at room temperature and presents a blue luminescence band with a fast lifetime of 600ns.