Effects of Ag addition on sintering of a crystallizable CaOB2O3-SiO2 glass have been investigated at 700degrees-900degreesC in different atmospheres. With Ag content increasing in the range of 1-10 vol%, the softening point, the densification, the onset crystallization temperature, and the total amount of crystalline phase formed of the crystallizable glass are reduced when fired in air. A bloating phenomenon is observed when the crystallizable CaO-B2O3-SiO2 glass doped with 1-10 vol% Ag is fired at 700degrees-900degreesC for 1- 4 h. Fired in N-2 or N-2 + 1% H-2, however, the above phenomena disappear completely. It is thus believed that the diffusion of Ag into the crystallizable glass, which is caused by the oxidation of Ag in air, is the root cause for the above results observed.