The mixture of (opalit+Al) powder was ignited by electric shock for the preparation of sialon powder by changin the contents of Al. The formation reaction of sialon was investigated by heating the specimens of ignited mixture (opalit+Al) in nitrogen atmosphere at various temperature. The phases existing inthe specimens nitrided between 1400 and 1$600^{circ}C$ were found $eta$-sialon 15R-sia-lon $Al_2O_3$ and AlN but the mixture $eta$-sialon and 15R-sialon was finally acquired by heating the ignited mixture of (Al 50%+opalit) at 175$0^{circ}C$ for 3hours in nitrogen atmosphere.