Na-borosilicate glasses are used widely in glass-matrix composites which are produced by slurry or sol-gel infiltration followed by hot-pressing. The hot-pressing behaviours of the glass powders are an important parameter in the preparation of the glass-matrix composites. The densification and crystallization of the gel and melt-derived Na-borosilicate glass powders under hot-pressing were studied. Gel-derived powders crystallized faster than the melt-derived powders. Cristobalite was the crystalline phase in both powders. The crystallization of the gel and melt-derived powders inhibited the viscous sintering during hot-pressing. Viscosities of the powders were calculated at various temperatures under isothermal hot-pressing conditions. Melt-derived powders had lower viscosities then the gel-derived powders. (C) 1997 Elsevier Science Limited and Techna S.r.l.