Objective To investigate the expression and significance of c-Jun N-terminal kinase (JNK) and c-Jun in the experimental rat thoracic aortic aneurysm. BR>Methods Twenty adult male Wistar rats were randomly divided into two groups: sham group and operated group. The thoracic aortic aneurysm models were induced by CaCl2 The thoracic aortic segments were collected at the 4th week after surgery. Immunohistochemistry and Western blotting were performed to detect the expression of JNK and c-Jun in the wall of the aneurysm. Results Immunohistochemical staining results showed that p-JNK and p-c-Jun were located extensively in smooth muscle cells of the tunica media in the aortic aneurysm, while there was only a little positive staining in the control group. Western blotting results indicated that the expression levels of p-JNK and p-c-Jun in the aortic aneurysm were higher than those in the control. Conclusion The expressions of p-JNK and p-c-Jun in thoracic aortic aneurysm are stronger than that in the control. The JNK/c-Jun pathway may play a significant role in the development of aortic aneurysm. BR>