The objective of this study was to produce buttermilk fortified with calcium, magnesium, and whey protein by adding some selected calcium and magnesium salts, and a whey protein concentrate (WPC 68) into the milk being processed prior to its re-pasteurization. At the first stage of the study, various amounts of calcium salts (calcium lactate, calcium citrate), magnesium salts (magnesium gluconate, magnesium hydroasparaginate), and WPC, or their mixtures, were added into the milk samples. Their impact on the thermal stability of milk during the 15 second repasteurization at 74°C was determined. After the thermal processing of milk, its pH value was measured and it was found that clots of proteins were formed. It was proved that when a mixture made of calcium citrate, magnesium hydroasparaginate, and magnesium gluconate was applied, it was possible to fortify the milk being processed with, at least, 72 mg% of calcium and with about 30 mg% of magnesium. The addition of the indicated amounts of the two above mentioned salts did not cause the milk proteins to coagulate during the milk re-pasteurization, and the active acidity of milk was higher than 6.52. At the second stage of the study, under the laboratory conditions, buttermilk was produced from the milk fortified with the selected elements according to the formula developed at the first stage. The additives were added into the milk before its re-pasteurization (74 ºC/15 s). During the refrigerated storage of the buttermilk produced, its sensory and physicochemical properties deteriorated. The strongest changes were found in the buttermilk samples fortified with calcium citrate, magnesium gluconate, and WPC. It was proved that the most favourable solution was to produce buttermilk fortified with calcium salts, magnesium hydroasparaginate, and WPC.