Nano-yttrium oxide has been synthesized from yttrium nitrate hexahydrate by combustion of Agarics bisporus (mushroom) used as fuel. The precursor yttirium nitrate and fuel in acid medium are combusted in furnace at 400 ºC for 3 h yields yttria nanopowder. Morphology of the reaction products are characterized by SEM and TEM. Synthesized yttria nanoparticle are characterized by UV, FTIR, XRD and EDAX are discussed. The crystallite size obtained nano yttria particles are calculated by Scherer′s equation and compared with Williamson-Hall method.