Abstract: Provided are: a method for manufacturing a glass substrate for a magnetic disk by using an alternative abrasive having the same polishing performance as cerium oxide, which has conventionally been used as an abrasive for polishing principal faces of glass substrates for magnetic disks; and a method for manufacturing a magnetic disk. At the time of polishing a principal face of a magnetic disk glass substrate by using a slurry, the disclosure employs a slurry containing: an abrasive made of granular zirconia; a first additive including a phosphate and/or a sulfonate; and a second additive including a re-aggregation inhibitor.