To study microstructure of Na2O-B2O3-SiO2-Al2O3 glass, which is a starting material for preparing porous glass, B-11 one-dimensional (1D) magic-angle spinning (MAS) spectra and results of two-dimensional (2D) B-11-B-11 homonuclear correlation experiment under MAS are examined at 21.81 We conclude that two of the four peaks observed for B-11 are assigned to borate rings, which we assign as the main components in the boron-rich phase to be removed by acid leaching.