A mass-spectrometric Knudsen effusion method has been applied to study the vaporization behavior of three cesium-containing borosilicate glasses in the temperature range 845–1150 K. Vapor species of CsBO2(g) and Cs2(BO2)2(g) have been identified for the glass containing Cs2O, and NaBO2(g), Na2(BO2)2(g) and NaCs(BO2)2(g) have been identified in addition to CsBO2(g) and Cs2(BO2)2(g) for glasses containing Na2O and Cs2O. The vapor species of Na(g) has been further observed in the initial stage of heating to 1000 K. for the glass in which the mole ratio of Na2O plus Cs2O to B2O3 is larger than unity, while no vaporization of Na(g) occurs for the glass in which the ratio is equal to unity. Enthalpies of vaporization, enthalpies of formation and dissociation energies for the vapors and chemical activities of pseudo components in the glasses have been determined from the measured partial pressures and discussed by comparing with those for sodium borosilicate glasses, NaBO2(s) and CsBO2(s).