Provided is a method for manufacturing low-phosphorus whey, said method including: a step in which a whey liquid, the starting material, is desalted by nanofiltration to obtain a low-chlorine whey liquid with a chlorine content reduced to at most 30 mmol per 100 g of solid content; and a step in which the low-chlorine whey liquid is passed through an ion-exchange resin to obtain an ion-exchanged whey liquid having a reduced phosphorus content. The aforementioned ion-exchange resin comprises an anion-exchange resin. At least a chlorine anion-exchange resin is used as the anion-exchange resin. The provided method can reduce the phosphorous content of whey while minimizing loss of the calcium and magnesium that whey contains.