We report room-temperature broadband laser emission in the near-ultraviolet to the blue-green spectral range using color centers in MgO microcrystals. The lasing MgO microcrystals are obtained through a solid phase reaction between SiO and Mg at 450 degrees C in an argon atmosphere and are mostly composed of an accumulation of microcubes enclosed by [100] facets. The laser action was observed in the wavelength region from 350 to 600 nm without using cavity mirrors. In the present MgO microcrystals, some of the color centers will be stabilized at the interfaces and/or boundaries of the microcrystalline domains, probably explaining the stable laser action even at room temperature.