The main object of investigations in this work is the chicken eggshells. The effective high-energy milling (HEM) treatment and utilization of chicken eggshells (ES) as a bio-waste waste have been investigated in environmental and economic interest. The composition of the ES includes mainly inorganic (94 % calcium carbonate as calcite, 1 % calcium phosphate and 1 % magnesium carbonate) as well as organic matter (4 %). During HEM, the mechanical activation process takes place, which leads to improvement of materials properties. The HEM-activated ES samples were characterized by thermal analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. The decarbonization was carried out using the thermal methods with Ar flow gas. We established that the thermal properties of the ES samples change considerably due to HEM treatment. The changes appear as: (1) shifting of decarbonization temperature of HEM-activated samples to lower temperature of about 30 °C; (2) decrease in mass losses and temperatures of decomposition with the increasing milling time; and (3) decrease in DTA peak areas for the all HEM-activated samples. As was shown earlier, the HEM treatment has a beneficial effect on the application of the ES. They can be used as: sorbents and soil improvers (separately or as mixtures with apatite minerals or appropriate technogenic wastes, containing main for the plants nutrients—N, P, K, S, Ca et al.).