The objective of the research study was to determine the content of selected macroelements and microelements in acid casein and caseinates. The research materials comprised acid casein produced using a traditional method and sodium caseinate, calcium caseinate, and sodium-calcium caseinate produced using a method of extrusion. The analyzed protein preparations came from the industrial manufacturing. In the acid casein and caseinates, the water content was determined as were the mineral compounds in the form of ash, and the active acidity was measured. The samples of protein preparations were wet-mineralized, and, next, the contents of selected macroelements (Ca, P, Mg, K, Na) and microelements (Fe, Zn, Cu, Mn) were determined. The contents of Ca, Mg, Fe, Zn, Cu, and Mn were determined using a flame atomic absorption spectroscopy (flame: acetylene-air). The contents of K and Na were determined using an emission spectrometry (flame: acetylene-air). The content of P was determined using a colorimetric method. It was proved that the caseinates produced by extrusion had, on average, a lower water content (5.63 ÷ 6.28 %) than the acid casein produced by a traditional method (8.15 %). The caseinates contained a several times larger amount of ash (3.80 ÷ 4.54 %) compared to the acid casein (0.77 %). The protein preparations analyzed differed significantly in the pH value. The mean pH value of the acid casein was 5.10 and that of calcium caseinate: 6.92. Compared to the acid casein and regardless of their type, the caseinates contained much more calcium (respectively: 1.196 ÷ 22.004 mg/g d.m. vs. 0.499 mg/g d.m.), potassium (0.136 ÷ 0.262 mg/g d.m. vs. 0.005 mg/g d.m.), and sodium (0.279 ÷ 12.665 mg/g d.m. vs. 0.005 mg /g d.m.), and the similar concentrations of phosphorus (8.084 ÷ 8.177 mg/g d.m. vs. 8.205 mg/g d.m.) and magnesium (0.033 ÷ 0.040 mg/g d.m. vs. 0.039 mg/g d.m.), except for the calcium caseinate. The calcium caseinate was characterized by the highest content of calcium and a nutritionally desirable calcium-tophosphorus ratio (2.70 : 1), which indicated that it could be used as a food additive to enrich food products with the high-quality protein and calcium. Regarding the microelements, the caseinates contained higher amounts of iron (respectively: 76.234 ÷ 89.325 μg/g d.m. vs. 8.090 μg/g d.m.) and manganese (0.654 ÷ 6.068 μg/g d.m. vs. 0.155 μg/g d.m.) compared to the acid casein. The sodium-calcium caseinate was characterized by lower contents of zinc (17.042 μg/g d.m.), sodium caseinate (29.508 μg/g d.m.), and calcium caseinate (28.602 μg/g d.m.) compared to the acid casein (27.101 μg/g d.m.). The calcium caseinate had more copper (1.801 μg/g d.m.) than the acid casein (1.284 μg/g d.m.), sodium caseinate (1.234 μg/g d.m.), and sodium-calcium caseinate (1.120 μg/g d.m.).