Adult Brown Norway (BN) rats exhibit numerous internal elastic lamina (IEL) ruptures in the abdominal aorta (AA) and a lower aortic elastin-to-collagen ratio (E/C) compared with other strains. We studied here AA mechanical properties in BN compared with control strains. AA stiffness (assessed by plotting elastic modulus/wall-stress curves obtained under anesthesia), thoracic aorta elastin and collagen contents, and IEL ruptures in AA were measured in male BN and LOU rats aged 6, 10, and 15 wk. The Long Evans (LE) control strain was compared with BN at more advanced ages (15, 28, and 64 wk). At all ages, aortic E/C was lower in BN than in control strains. At 6 wk, AA stiffness was greater in BN than in LOU. In both strains, AA stiffness decreased between 6 and 10 wk, more so in BN than in LOU, and then increased, reaching similar values at 15 wk. BN AA stiffness was not different from that of LE at 15 and 28 wk, but was significantly lower at 64 wk. The increased stiffness in young BN rat AA may be due to the decreased E/C. IEL rupture onset in the BN around 7-8 wk, which decreases stiffness, as suggested by its pharmacological modulation, abolished such differences by 15 wk. Thereafter, age-related AA stiffness increased less in BN than in LE, likely due to the numerous IEL ruptures. We conclude that, in the BN rat, the lower E/C and the presence of IEL ruptures have opposing effects on arterial stiffness.