The effect of ageing treatment and coarse intermetallic particles on the compromise between the toughness and the yield strength of 7010 and 7150 aluminum alloys (Al-Zn-Mg-Cu alloys) are investigated. Plane-strain fracture toughness tests were performed on the compact-tension specimens of L-T orientation. The fracture toughness of 7010 alloy was higher than that of 7150 alloy at the same ageing treatment. The 7150 alloy contain a greater amount of coarse Cu-bearing particles, which deteriorate the fracture behavior and decrease the ageing hardening ability of the alloy. The toughness of the both alloys increased greatly for the overaged condition as compared to that for the T6 condition. Two dominant mechanisms of failure occur: microvoid-induced transgranular fracture and intergranular fracture modes, and the former becomes more important in the overaged ageing conditions.