The tensile properties and plane-stress fracture toughness of AA6156 aluminum alloy with different aging treatments were studied. The results show that the natural aged AA6156 alloy obtains perfect fracture toughness, while a lower strength. The AA6156 alloy in single peak aging at 175 oC and in 175 oC/6 h+190 oC/13 h duplex over aging can both offer preferable strength, while lower fracture toughness. The property of the alloy can achieve the superior combination of the strength and toughness under 175 oC/2 h+200 oC/0.5 h aging conditions. Microstructure observations indicate that pre-aged treatment can increase the quantity of GP-zones, thus promoting homogeneous precipitation of β″ phase in the following aging treatments. The effect of aging treatments on fracture toughness of AA6156 alloy mainly depends on the strengthening phase β″ in the matrix, whereas grain boundary microstructures have less effect on it