Abstract: A glass-ceramic for substrate of magnetic disks having high strength can be obtained by subjecting to heat treatment a base glass comprising, in terms of weight percent of their oxides, from 65% to 80.0% of SiO2, from 0.5% to 5.0 % of Al2O3, from 13.0% to 19.0% of Li2O, from 1.0% to 7.0% of P2O5, from 0.5% to 10.0% of Y2O3 and from 0.2% to 2.0% of at least one of Sb2O3 and As2O3, and the glass-ceramic comprises Li2O·2SiO2 as the main crystal phase. The glass-ceramic has a bending strength of 230-36O Mpa and a surface roughness of less than 10 Angstroms after final polishing, and is thus suitable for use as substrate of magnetic disk. A process for producing the glass-ceramic is also provided.