It is believed that fly ash could be suitable for preparing the sialon by carbothermal reduction method because the total amount of SiO2 and Al2O3 is above 80% and the unburned residual carbon is above 5% within the fly ash. The effects of reaction temperature (1350, 1400, 145$0^{circ}C$) reaction time (1, 5, 10 hours) and the amount of carbon additions (C/SiO2=2, 3, 4 mole) on the $eta$-sialon synthesis were obserbed, It was conformed that $eta$-sialon (Z=2.15~2.18) was formed as major phase under all of the synthesis conditions and small amount of Si2ON2 SiC, AlN and Si3N4 was formed depending on the synthesis conditions. FeSix intermetal-lic compound was formed above 140$0^{circ}C$ reaction temperature due to the large amount of iron oxides within the raw fly ash.