Abstract: The influence of the composition of boron-containing alloys: ferroboron and complex modifier (ferrosilicomanganese with boron) on the microstructure and mechanical properties of the processed steel is studied. High-temperature laboratory experiments on steel alloying with boron-containing ferroalloys have been carried out to obtain samples of the 26CrMoVN tube of steel. The degree of boron absorption by steel was studied using various boron-containing ferroalloys. The microstructure, mechanical characteristics and contamination with nonmetallic inclusions of the processed steel were determined. It is shown that the use of ferrosilicomanganese with boron allows to achieve a higher (82%) degree of boron absorption by metal in comparison with the use of standard ferroboron (44-52%). Also noted higher mechanical properties (tensile strength, yield strength, elasticity) of the resulting metal, greater purity of nonmetallic inclusions and stable results on the grain size of steel are noted, which is a good characteristic of the complex modifier influence on the structure of the processed metal.