The effect of aging on the mixed-mode I/III fracture toughness was evaluated for two 2034 Al type alloys with different Mn content. The effect of aging was found to be significantly different in the two alloys. Alloy 1 which had < 0.1 wt% Mn exhibited a significant reduction in fracture toughness with increasing mode III loading contribution. In this alloy, increasing aging time resulted in less reduction of fracture toughness with increasing mode III loading contribution. On the other hand, alloy 2 which had 1.08 wt% Mn exhibited a marginal effect of mixed-mode loading on fracture toughness. In this alloy increasing aging time did not result in a significant change in the mixed-mode fracture behavior. The results are discussed in light of the microstructures, fracture mechanisms and deformation field ahead of the crack tip under mixed-mode loading.