${eta}$-Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350$^{circ}C$ in N2-H2 atmosphere, using graphite as a reducing agent. The synthesized ${eta}$-Sialon powder was pressurelessly sintered over 1450-1850$^{circ}C$ in nitrogen atmosphere. The average particle size of ${eta}$-Sialon powder was about 4.5$mu extrm{m}$. The relative density, M.O.R., fracture toughness and micro-hardness of ${eta}$-Sialon ceramics sintered at 1800$^{circ}C$ for 1 hour were 92%, 36 kpsi, 2.8MN/㎥/2 and 13.3 GN/㎡, respectively. The critical temperature difference (ΔT) in water quench thermal shock behavior showed about 375$^{circ}C$ for the synthesized ${eta}$-Sialon ceramics.