Phase transformation and microstructural change of a furnace-cooled eutectoid Zn-Al alloy specimen (76 wt % Zn-22 wt % Al-2 wt % Cu) were investigated during creep testing by using scanning electron microscopy and X-ray diffraction techniques. Creep-induced decomposition of a metastable T’ + eta, occurred during the creep testing. Also microstructural change was observed from a lammellar structure partially into a spheroidized structure in the rupture part of the furnace-cooled alloy. The mechanism of the creep rupture of the furnace-cooled eutectoid Zn-Al alloy was also discussed.