Abstract: A process for preparing a glass or glass-ceramic composite sintered body by a sol-gel method comprises reacting(A) at least one silicic acid ester represented by the general formula (I). ##STR1## wherein R.sub.1 to R.sub.4 are each hydrogen or a group represented by Chd xH.sub.2x+1 (OC.sub.2 H.sub.4).sub.y - wherein x is 1 to 5, and y is 0 to 10, provided that R.sub.1 to R.sub.4 are not all hydrogen at the same time, and n is 0 to 20;(B) at least one phosphorus compound represented by the general formula (II), (III) or (IV): ##STR2## wherein R.sub.5 to R.sub.9 are each hydrogen, an alkyl group having 1 to 5 carbon atoms, a phenyl group or an aralkyl group having 7 to 10 carbon atoms, and m is 0 to 10; and(C) at least one compound selected from the group consisiting of calcium salts and calcium coumpounds represented by the general formula (V)Ca(OR.sub.10).sub.2 (V)wherein R.sub.