Effects of Mg, Cu and Si on the bake-hardening of Al-2-3 mass%Mg alloys were investigated by the tensile testing, hardness measurments and electron microscopy. The strength in as-solution-treated condition and the bake-hardenability increased with Cu addition up to 0.6%. Although the as-solution-treated strength did not change with Si content, bake-hardenability increased by small addition of 0.1%Si. High bake-hardenability in Al-2-3%Mg alloys with Cu and Si additions was due to the fine and homogeneous GPB zone formation. Cu increased the density of GPB zone in the baked condition at 447K for 1.2ks, whereas Si suppressed dislocation loop formation which would otherwise enhance the inhomogeneous precipitation of the S' phase. In Al-2-3%Mg alloys with small additions of Cu and Si, the hardening during room temperature aging is small, thus these alloys are expected to have a great advantage in the automobile body panel use.