Aim To study the expression and significance of cathepsin B and Cystatin C in vascular smooth muscle cells (VSMC) of patients with abdominal aortic aneurysms (AAA) and to investigate underlying roles in pathogenesis of AAA. Methods 21 cases of AAA and 8 cases of normal abdominal aortas were collected in this study. HE staining and immunohistochemical technique were used to evaluate the change of cathepsin B and Cystatin C in the media of AAA. Results Immune reaction of cathepsin B was positive in the AAA,and immune reaction of Cystatin C was positive in the normal abdominal aortas. The positive cells were mainly localized in the smooth muscle cell (SMC). Imagine analysis results showed that the MOD value of cathepsin B in SMC of AAA evidently increased,while Cystatin C evidently decreased. There were significant differences in cathepsin B and Cystatin C between the AAA and normal abdominal aortas. Conclusion The expression of cathepsin B promoted and expression of Cystatin C reduced in the SMC of AAA. An imbalance between cysteine cathepsins and their inhibitor may cause the excessive breakdown of extracellular matrix (ECM) in the arterial walls leading to the progression and rupture of AAA.