Abstract: Effects of Mn and Si contents on microstructure and mechanical properties of the new-type Al-Mg-Si-Cu alloy were investigated by scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and transmission electron microscopy (TEM). The results showed that the age-hardenability of the alloy decreases with increasing Mn content. When adding 0.35% Mn to the alloy, the ultimate tensile strength (Rm) changes little while the yield strength (ReL) and elongation (Ae) increase significantly. When adding 0.7% Mn to the alloy, both the strength and elongation decrease because the volume fractions of both coarse insolube constituents and fine dispersoids increase simultaneously. With the Si content increases, the age-hardenability of the alloy is improved with increasing Rm and decreasing ReL and Ae especially, the density of the age-hardening phase β″ precipitates increase.