To produce a glass substrate for magnetic disk medium, excellent in surface smoothness and flatness and suitable for magnetic disk dealing with turning to low floating height of a magnetic head, and further to provide a production method thereof.

The glass substrate is subjected to a grinding treatment, a chemical strengthening treatment and regrinding treatment in order. The decreasing amount in the thickness direction of the glass substrate by the grinding after the chemical strengthening treatment is regulated so as to be 0-0.4 μm by one face, and the surface roughness on the surface of the glass substrate is regulated so as to be ≤0.5 nm Ra and ≤5.0 nm Ry. Further, the flatness of the surface of the glass substrate is regulated so as to be ≤3 μm.