A method of manufacturing a low-phosphorus whey, the method including subjecting a raw whey liquid to a demineralization treatment using a nanofiltration method to obtain a low-chloride whey liquid in which the chloride content has been reduced to not more than 30 mmol per 100 g of solids, and passing the low-chloride whey liquid through an ion exchange resin to obtain an ion-exchanged whey liquid having a reduced phosphorus content, wherein the ion exchange resin is composed of an anion exchange resin, and at least an anion exchange resin in chloride form is used as the anion exchange resin. The method of manufacturing a low-phosphorus whey can reduce the phosphorus content within the whey while suppressing reduction in the calcium and magnesium content.