η' Meson as a pseudoscalar gluonium

QCD sum rules induced by the current G_μν^aG_μν^a constructed from gluon field operators are derived. Saturating the sum rules by η' rough estimates for the η' mass and its residue are found. The difference between the η' and typical quark states such as ϱ is noted. Breaking of the opeator expansion by the instanton effects is discussed.