W–1% La2O3 alloy is considered as one of the candidate material for plasma-facing components of future fusion reactors. The phases of as-forged W–1% La2O3 alloy, especially the nano-sized particle phases, have been investigated using transmission electron microscopes．Eight kinds of particle phases have been found in the alloy. They are: three kinds of La2O3 phases; two kinds of WO3 phases; W3O8 phase; La0.14WO3 phase and (La2O3)5WO3 phase. La2O3, WO3 and W3O8 are dominant nano-sized phases in the alloy. These particles have sizes ranging from about 20 nm to about 100 nm. The possible formation processes of these particle phases are also discussed.