Effect　of　Cu　content　on　microstructure　and　properties　of　Al-2.5Mg-xCu-0.2Si　alloys　was　investigated　in　this　research.　Results　show　that　the　microhardness　of　the　alloy　with　Cu　addition　has　an　obvious　rapid　hardening　effect　due　to　the　clustering　of　Cu　and　Mg　at　the　early　stage　of　aging.　With　further　aging,　the　microhardness　of　the　alloy　increases　again　and　reaches　an　obvious　second　peak　due　to　the　formation　of　S＇　phase　and　Guinier-Preston-Bagaryasky　(GPB)　zone.　The　increasing　amount　of　Cu　content　results　in　a　significant　increase　in　tensile　strength　and　yield　strength　while　a　reduction　of　elongation　and　intergranular　corrosion　performance.　With　the　increase　of　Cu　content,　the　intergranular　corrosion　performance　of　the　alloy　becomes　worse.　The　alloy　has　a　reasonably　well　corrosion　performance　when　the　Cu　content　is　less　than　1.14wt%.　However,　there　is　a　significant　reduction　when　the　alloy　contains　2.10wt%　Cu.　Based　on　these　results,　the　alloy　containing　1.14wt%　Cu　has　better　mechanical　properties　and　corrosion　resistance.