Mixtures of very small amounts of additive, carbon and silica(about 0.46${mu}{ extrm}{m}$) which synthesized by the hydrolysis of ethyl silicate, the molar ratio of SiO2/C was fixed to 1/10, was nitrided at 145$0^{circ}C$. It was considered that the optimum amount of additive to promote the nitridation reaction was below 2.0wt%. By the addition of additive, the nitridation reaction was promoted and formation of $eta$-Si3N4 was promoted at 145$0^{circ}C$ for 1hour, but, the nitridation reaction was decreased and the ratio of $alpha$/$eta$ of Si3N4, was increased at 145$0^{circ}C$ for 5 hours. The crystal phase was $alpha$ phase and the nitridation reaction was promoted and the particle size of silicon nitride was become smaller by the addition of $alpha$-Si3N4, but silicon nitride of whisker-like form was produced by the addition of transition elements. There was a difference in the lattice constants of $alpha$-Si3N4, but no difference in its of $eta$-Si3N4 according to kinds of added substance and reaction time.