In order to prepare the functional porous glasses, fabrication of foaming glass materials was achieved utilizing the hydrothermal treatment. In the present paper, SiO2-Na2O-B2O3 glass was hydrated by the hydrothermal hot pressing of the glass powder mixed with pure water under the condition of loading pressure of 40 MPa and heating up to 523K. The hydrothermally treated glass contained 10.8 mass% of water. By heating up to 473 K, it started to foam by releasing water and the porous structure was obtained. The minimum apparent density was obtained to be 0.25 g /cm3 after the heat treatment at 673 K for 300 s. It was clarified that the prepared hydrated glass with the hydrothermal treatment would be promising for fabricating the porous glass materials by firing at low temperature.