Glasses of the compositions Li₂O • 3B₂O ₃ and Cs₂O • 3B₂O₃ have been investigated using X-ray diffraction. The isomorphous substitution of heavy cesium for light lithium makes it possible to rather accurately determine the B-O and O-O interatomic distances in the lithium-containing glass and the Cs-Cs interatomic distances in the cesium-containing glass. For the Li₂O • 3B₂O₃ glass, ten coordination shells are observed in the ordering region up to 7 Å. A comparison of the experimental and model atomic radial distribution functions has revealed that the structure of the glass contains groups similar to those observed in crystalline LiB ₃O₅. They include at least two triborate groups bound via the oxygen atom. For the Cs₂O • 3B₂O₃ glass, ten coordination shells are revealed in the ordering region up to 12 Å. An analysis of the experimental atomic radial distribution curve in the framework of the fragmentary model has allowed the conclusion that cavities similar to those inherent in crystalline CsB₃O₅ are retained in the structure of the cesium-containing glass and contain up to three cesium atoms located at distances close to the corresponding distances in the crystal. The statistical mean coordination of the cesium atoms by oxygen atoms remains unchanged.