This study evaluates the effect of including whey at different inclusion rates on the chemical composition and mineral profile of maize silage. Five whey inclusion rates (0%, 2.5%, 5%, 7.5%, and 10% w/w of fresh forage) were tested in a completely randomized design with five replicates. After 80 days of ensiling, samples were analyzed for moisture, dry matter, crude protein, neutral detergent fiber, acid detergent fiber, ash, and the concentrations of calcium, phosphorus, magnesium, potassium, and sodium. Whey inclusion rates significantly increased ash content, reflecting the mineral contribution of this by-product, particularly sodium and potassium. Sodium (Na) concentration followed a quadratic response (p < 0.05) to whey inclusion rates, reaching a minimum at 3.16% whey. Magnesium (Mg) concentration decreased linearly, possibly due to dilution, leaching, or chemical interactions during ensiling. In contrast, moisture, dry matter, crude protein, and fibrous fractions did not significantly differ among treatments, indicating that whey at the tested inclusion rates does not affect cell-wall constituents or crude protein content of the silage. The results indicate that whey can be used as a mineral source in maize silage, increasing mineral content and potentially improving ensiling characteristics. However, high whey inclusion rates should be avoided to prevent excessive sodium concentrations and possible mineral imbalances. Whey represents a viable option for maize silage production when applied at controlled inclusion rates and when its impact on the overall diet of ruminants is considered.