The behaviour of silica during the carbothermal reduction nitriding process at temperatures between 1300-1500°C was studied by means of X-ray diffraction and scanning electron microscope analysis. The experimental runs were allowed to proceed up to 1 h in presence of nitrogen flow. The following mechanism of reduction nitriding of silica which was based on the experimental observation was proposed. Initially the impurity of the starting material is reduced before 1300°C. SiO2 was reduced into SiO gas phase by active carbon and it was vaporised out of the mixture. The nucleation of α-Si3N4 was formed vapour-gas reaction took place and deposited on the surface of the mixture as well as around the reaction crucible. In the third stage, α-Si3N4 transforms to one dimensional direction which was β-Si3N4 particle. This was followed by the formation of SiC at temperature above 1450°C.