0.3%Er is added to Al-5.6Zn-1.9Mg-1.6Cu-1.0Li alloy (in wt.%) to investigate the effect of erbium on microstructure of the alloy. Most of erbium exists in the primary Al3Er phases which are incoherent with the alloy matrix unevenly. A few of fine Al3Er phases, precipitated from supersaturated solid solution, are coherent with the matrix. η′-MgZn2 precipitates in the single-aged alloy are sparser than that in the double-aged alloy. A few of fine Al3Er phases act as the heterogeneous sites of η phases. There exist some precipitation free zones in the matrix around fine Al3Er precipitates. Erbium is segregated to grain boundary seriously. A few of Al3Er phases are present in grain boundary. The grain boundary precipitates are not continuous about the Al3Er phases.