Mesenchymal stromal cells (MSCs) are universal regulators of regenerative processes due to their ability to secrete regulatory molecules or replace dead cells through differentiation in the appropriate direction. Recently, another mechanism for the beneficial effects of MSCs on damaged tissue has been discovered, such as the transfer of mitochondria into its cells in response to stress signals. MSCs can transfer mitochondria through tunneling nanotubes that form a communication bridge between cells, through gap junctions, by release as part of extracellular vesicles or in free form, and as a result of complete or partial fusion with recipient cells. In damaged cells that received mitochondria from MSCs, impaired energy metabolism is restored and oxidative stress is reduced, which is accompanied by increased survival, and in some cases also increased proliferation or a change in differentiation status. The restoration of energy after the transfer of mitochondria from MSCs has a beneficial effect on the functional activity of recipient cells and suppresses inflammatory reactions. A significant contribution of the MSC mitochondrial donation to the therapeutic efficacy of MSCs has been repeatedly demonstrated in models of damage to various organs in experimental animals. This stimulates the search for methods to enhance the process of mitochondrial donation. However, it should be taken into account that MSCs are able to transfer mitochondria to malignant cells as well, thereby stimulating tumor growth and increasing its resistance to chemotherapy. These data make it necessary to evaluate the prospects for the use of MSCs in cell therapy with caution. On the other hand, they can serve as a basis for the search for new therapeutic targets in the treatment of oncological diseases.