Abstract A series of Cs-borosilicate glasses of general formula (mol%): 17.5Na 2O–2.5Cs 2O–45SiO 2–(35- x)B 2O 3– xCaO, where x varies from 0 to 10, were prepared by conventional melt quenching technique. Physicochemical properties like glass transition temperature, extent of volatilization loss of Cs and chemical durability of these glasses have been investigated in detail. Based on the T g values obtained from DSC studies, it is confirmed that the glass network remains unaffected with increase in CaO content in the glass at the expense of B 2O 3. Cs loss as function of duration of heating revealed that the Cs evaporation follows diffusion controlled mechanism and the extent of loss increases with the increase of CaO incorporation in glass. Chemical durability of the glasses has been found to improve significantly with in the increase of CaO content in glass and this has been attributed to the formation of Ca and Si rich layer at the outer surface of the glass, as inferred from SEM with EDX analysis.