A magnesium borate compound 2MgO . 3B2O3 . 17H2O has been synthesized and its structure studied by IR and Raman spectroscopy as well as by thermal analysis. The structural formula of this compound was Mg[B3O3(OH)5] . 6H2O. Its solubility in pure water at 25-degrees-C, refractive index, thermodynamic properties, and X-ray powder diffraction data are reported.