Microstructural evolution and related phase transformation of an extruded eutectoid Zn-Al based alloy are studied in detail under creep deformation at 150℃. Lamellar structure in the extruded alloy spheroidized par­tially into fine grain structure. Also decomposition of a metastable η(1) T phase and a four phase transfor­mation. α+ε→T+η, were observed in the creep deformed alloy specimens. Creep rupture of the extruded Zn-­Al alloy was studied in correlating with the creep induced phase transformation and microstructural changes.