This paper presents the results of the entropy calculation of the equilibrium constants of chemical reactions at liquid-phase sintering of SiC ceramics with eutectic additives. The composition of the charge for sintering ceramics with nanoadditives forming the liquid phase was determined: MnO nano 1.5 wt. % + Al 2 O 3nano 2 wt.% + SiC µm 94 wt. % + SiO 2µm 2.5 wt. %. Possible chemical reactions of liquid-phase sintering of ceramics at a temperature of 1800 °C in a weakly reducing CO medium were established. The values of the change in the Gibbs energy for all possible chemical reactions at a sintering temperature of 1800 °C were calculated by the method of entropy calculation of the equilibrium constants. The elements of the liquid phase and reinforcing additives were determined.The elements of the liquid phase and reinforcing additives were determined. The structure and properties of finished sintered ceramic samples were studied. Microstructural analysis of ceramics indicated its grain structure with an average grain size of ~10 µm. The main phase components of the ceramics based on silicon oxide were determined. It was found that the sample consists of three main phases: modification of the ring radical of silicate Si 3 O 6 , silicon dioxide SiO 2 and anorthoclase (SiAl)O 4 .