Glass-ceramics containing cordierite (2MgO-2Al(2)O(3)-5SiO(2)) as a crystal phase based on the glasses in the system MgO-Al2O3-SiO2 were investigated for the application to magnetic disk substrate for higher storage capacity. Parent glasses were prepared with CeO2 addition as a flux and were crystallized by a controlled 2-step heat treatment The maximum nucleation and crystal growth rates were 2.4 x 10(9)/mm(3) . hr at 800 degrees C and 0.3 mu m/hr at 915 degrees C respectively. Only alpha-cordierite was precipitated after heat-treatment. After nucleation at 800 degrees C for 5 hours prior to crystallization at 915 degrees C for 1 hour, the resulting crystal volume fraction and crystal size were 17.6% and 0.3 mu m, respectively. Heat-treated specimens through the above condition showed the optimum properties for magnetic memory disk substrates as follows.; Bending strength of 192 MPa, Vickers hardness of 642.1 kg/mm(2), thermal expansion coefficient of 39 x 10(-7)/K and surface roughness of 27 Angstrom.