For Ti40Zr25Ni8Cu9Be18 metallic glass, nanocrystal forms in the as-cast amorphous matrix during fast cooling from supercooled liquid, and precipitates from amorphous matrix during heating process. The thermal stability of the nanocrystals during homogeneous temperature is influenced by deformation temperature. At relative low deformation temperature (below Tx-40K), the nanocrystal is very stable. Contrarily, nanocrystal exhibits low thermal stability at relative high deformation temperature (above Tx-40K). Moreover, nanocrystal precipitated during heating process possesses better thermal stability than nanocrystal existed in as cast condition at the same deformation temperature.