Abstract: A transparent, semitransparent or opaline glass-ceramics containing calcium phosphate crystals uniform and very fine in grain size is obtained by heat-treating a glass essentially comosed of 38-52 wt % of SiO.sub.2, 4-16 wt % of P.sub.2 O.sub.5, 6-18 wt % of Al.sub.2 O.sub.3 (may partly be replaced by La.sub.2 O.sub.3), 20-33 wt % of CaO (may partly be replaced by MgO, BaO,SrO and/or ZnO), 4-17 wt % of ZrO.sub.2 (may partly be replaced by TiO.sub.2) and 0-0.5 wt % of alkali metal oxide(s), wherein the molar ratio of P hd 2O.sub.5 to ZrO.sub.2 is not greater than 3:1, at a temperature above the transition temperature and below the softening temperature of the glass. This glass-ceramics is excellent in refractoriness, electrical insulation resistance, chemical resistance and mechanical strength and has a relatively high coefficient of thermal expansion.