When mirror polishing is performed on a glass substrate by bringing a polishing pad into contact with the surface of the glass substrate while supplying a polishing liquid containing polishing grains to the substrate surface, the pH of the polishing liquid is maintained within a certain range or the agglomeration degree or dispersion degree of the polishing liquid is controlled. Consequently, an adequate mirror polishing rate can be maintained and there can be obtained a glass substrate having a good end shape.