To prevent rupture of abdominal aortic aneurysms (AAAs), current preventive treatments involve surgery or the deployment of an endovascular stent. The development of gene or cell therapies as alternative therapeutics to stabilize AAAs represents a challenge. In the present contribution, we investigate the effect of a mesenchymal stem cell therapy on the mechanical properties of the rat xenograft model of AAA. This model reproduces the arterial dilation of the aneurismal disease and has been much used to study the biological impact of different approached therapies. The arterial structure of healthy native rat abdominal aortas, diseased untreated and treated AAAs were subjected to axial extension and pressurization tests (biaxial mechanical tests) in a pressure myograph device. A nonlinear hyperelastic and incompressible mechanical model was used to identify and compare the material parameters for the three specimen types. Histological analysis enabled a correlation between the results and the microstructure of the arterial tissue and particularly the presence of a thrombus or a neointima layer. Stress distributions within the arterial wall should then be computed by finite element modeling in order to predict the risk of rupture of aneurysms.