The　microstructure　evolution　of　the　Mg-5Zn-0.63Er　(mass　fraction,　%)　alloy　containing　quasicrystalline　phase　(I-phase)　under　the　as-cast　condition　was　investigated　via　different　heat　treatments.　The　results　show　that　apart　from　the　precipitation　of　the　W-phase　particles,　the　I-phase　almost　dissolves　into　the　matrix　after　solid　solution　treatment　at　480　degrees　C　for　10　h　(T4　state).　The　solution-treated　alloy　was　aged　at　175　degrees　C　for　6-100　h　(T6　state).　The　ultimate　tensile　strength　of　the　peak-aged　alloy　is　approximately　261　MPa　companying　with　an　elongation　of　10.5%.　The　improvement　of　the　tensile　strength　is　mainly　attributed　to　the　presence　of　the　rod-like　MgZn2　particles.