Synthesis of $eta$-Sialon powder was attempted with carbothermal reduction of porous glass. The porous glass was prepared by heat and hydrothermal treatments of 9.32 Li2O.46.5B2O3.37.2SiO2.6.98Al2O3 glass. Carbon pyrolyzed from propane gas was deposited on the porous glass, thereafter activated carbon was added as reducing agents. The synthesized $eta$-Sialon powder was pressureless sintered at 175$0^{circ}C$ for 1hr in N2 atmosphere. The characterization of the $eta$-Sialon powder was performed with XRD, BET, SEM and particle size analysis. The sinterability and mechanical properties of the sintered bodies were investigated in terms of bulk density, M.O.R., fracture toughness, morphology of microstructure and etc. The reduction effect of deposited carbon was better than that of activated carbon mechanically added. The formation of SiC was precominant over that of Si2ON2 and $eta$-Sialon owing to low partial pressure of N2 inside the pore, wehreas on the surface of porous glass the formation of Si2ON2 and $eta$-Sialon were predominant. Thereafter, SiC reduced unreacted glass to be $eta$-Sialon. Single phase of $eta$-Sialon(Z=1.92) was obtained from PGA porous glass having the largest pore radius by the simultaneous reduction and nitridation method at 145$0^{circ}C$ for 5hrs. The bulk density, M.O.R., and KIC of the sitered body are 3.17g/cc, 434.4MPa and 4.1MPa.m1/2, respectively.