One of the effective ways to increase calcium level in cottage cheese can be the addition of calcium salts to the processing milk prior to its heat treatment (pasteurization). The objective of this investigation was to determine the impact of different calcium salts added on the heat stability and some physicochemical properties of processing milk used to manufacture cottage cheese. It was stated that water-soluble calcium salts added to the processing milk increased its acidity. The milk fortified by this measure showed a decrease in its heat stability, and, furthermore, milk proteins precipitated during its repasteurization. The highest quantity of water soluble salts added that did not cause the precipitation of proteins during the re-pasteurization was the addition of 0.15% anhydrous calcium chloride; thanks to this addition, the calcium content in the processing milk was increased by 55 mg%. An additional test for heat stability of milk proteins was carried out and its results indicated that with regard to milk proteins it was safer/more favorable to add 35 mg% of calcium (added in the form of a calcium chloride) or 20 mg% calcium (added in the form of other water-soluble calcium salts). The addition of water-insoluble calcium salts (calcium citrate or calcium carbonate) made it possible to distinctly increase the calcium level in processing milk without the negative effect of precipitating proteins. By adding even 5% of those calcium salts there was caused no decrease in the heat stability, and the protein coagulation during the milk repasteurization did not occur. It was determined that the incorporation of various calcium salts combinations into the processing milk provided higher calcium levels compared with single calcium salts added. When 63 mg% of calcium (in the form of calcium citrate) and 20 mg% of calcium (calcium lactate) were simultaneously added to the processing milk, the milk fortification results were improved (the calcium level rose by 83 mg%) if compared with the effect of adding single water-soluble calcium salts. The application of the mixes of salts as indicated above did not cause the precipitation of proteins.