Purpose. Theoretical and experimental research on the structural and strength peculiarities of the backfill mass formation during the ore deposits development by activating the binding material of the backfill mixture using fine grinding at the stage of its preparation. Methods. An integrated methodological approach is used, consisting of laboratory studies on determining the properties of backfill mixtures and the structural internal bonds of the backfill mass using scanning electron microscopy. Some laws of the binding material chemistry are used and systematized in the course of theoretical research. Findings. Based on theoretical and experimental research, the interaction and the hydration products of the backfill mixture binding components with water have been studied. The use of a finely ground combined binding material made of slags and limestone improves and strengthens the structural bonds of the backfill mass through a large gap in the covalent bonds of silica and slags, the transition of ions of a weak ionic bond to the formation of other compounds and equalizing the ratio of Si and Са ions in solution. Originality. It has been determined that with an increase in the specific surface area of the binding material particles, the shape of structural new formations of the backfill mass improves, has high strength, and the basicity of its new formations increases. Practical implications. Using the results, it is possible to rationally choose the binding material dispersion, obtain high strength of the backfill mass and increase the stability of its outcropping.