The　microstructure　and　properties　of　three　different　Al-Zn-Mg-Cu　alloys　with　high　Zn　content　(9　wt　pct,　10　wt　pct,　and　11　wt　pct,　marked　as　9Zn,　10Zn,　and　11Zn,　respectively)　were　investigated.　The　strength　of　alloys　increases　as　the　Zn　content　increases　from　9　wt　pct　to　10　wt　pct,　while　it　does　not　increase　any　more　as　the　Zn　content　increases　continuously　from　10　wt　pct　to　11　wt　pct.　The　stress-corrosion　cracking　(SCC)　resistance　decreases　as　the　Zn　content　increases　from　9　wt　pct　to　10　wt　pct,　while　it　changes　unobviously　as　the　Zn　content　increases　continuously　from　10　wt　pct　to　11　wt　pct.　The　elongation　and　fracture　toughness　of　alloys　decrease　as　the　Zn　content　increases　in　these　Al-Zn-Mg-Cu　alloys.　The　Zn　content　has　little　effect　on　the　precipitation　reaction　of　Al-Zn-Mg-Cu　alloys　that　contain　the　mixture　of　GP　zones,　and　eta＇　are　the　main　Matrix　Precipitates　(MPt)　in　the　peak-aging　state,　and　the　mixture　of　eta＇　and　eta　are　the　main　MPt　in　the　over-aging　state.　The　amount　of　MPt　and　coarse　T　(AlZnMgCu)　phases　are　shown　to　increase　with　the　increasing　Zn　content　in　Al-Zn-Mg-Cu　alloys.　The　coarse　T　phases　hardly　dissolve　into　the　matrix　and　are　the　source　for　the　crack　initiation,　which　may　be　the　responsibility　for　the　negative　effect　on　the　properties　of　high　Zn　content　Al-Zn-Mg-Cu　alloys.