Abstract This article discusses the behavior of the Si 3N 4+SiC mixture during sintering. The purpose of this study was to obtain data on sintered Si 3N 4/SiC composites. The proportion of Si 3N 4 and SiC powders in the initial mixtures varied from 0% to 100%, while the molar ratio of SiO 2/Y 2O 3 was 2:1 and the total amount of additives (14 wt.%) was kept constant. Samples of the powders were pressed under 300 MPa and heated to 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950 and 2000 °C, in a nitrogen atmosphere, and allowed to cool as soon as this temperatures were reached. After the heating step, the samples were characterized according to their final density, crystalline phases, microstructures and weight loss. The samples displayed little weight loss, but their density decreased with increasing amounts of SiC, particularly at temperatures above 1750 °C. All the mixtures showed the formation of liquid phase between 1650 and 1750 °C, regardless of their composition.