The effects of aging treatments on the mechanical properties and corrosion behavior of 6156 A1 alloy were investigated by means of hardness measurement, conventional tensile test, slow strain rate tensile tests (SSRT) and intergranular corrosion test. The microstructures were observed with TEM. The results show that in T6 under-aging (T6UA) condition the precipitates are GP zones with high density in matrix, and no distinct grain boundary precipitates are observed. In T6 peak-aging (T6PA) condition the precipitates are β″ phase with high density and small amount of Q′ phase in matrix, the grain boundary precipitates are continuously distributed. The strength of T6 peak-aged 6156 alloy is the highest, however it has the serious tendency to intergranular corrosion and very high sensitivity to stress corrosion crack. With the aging time increasing, Q′ phase increases and coarsens, the grain boundary precipitates are coarsened obviously and sparsely distributed, precipitate free zone ( PFZ) appears. In T78 conditions, there are plenty of Q′ precipitates in matrix, and the coarse and isolate precipitates present in grain boundaries, and the PFZ is broaden. So the corrosion resistance is obviously improved while tensile strength is a little decreased.