Objective To investigate the expression and significance of vascular endothelial growth factor（VEGF）and thrombospondin-1（TSP-1）in the experimental rat thoracic aortic aneurysm. Methods Thirty adult male Wistar rats were randomly divided into two groups: sham group and operated group. The thoracic aortic aneurysm model was induced by CaClSUB>2/SUB> . The thoracic aortic segments were collected at 4 weeks after surgery. HE staining and Orcein staining were used to observe histological changes in the thoracic aorta. Immunohistochemistry and Western blotting were performed to detect the expressions of VEGF and TSP-1 in the wall of aneurysm. Results Immunohistochemistry staining results showed that VEGF was mainly located in the tunica media and tunica adventitia in the aortic aneurysm and there was few positive staining in the control group. TSP-1 was located in the normal aorta but the positive staining in the aneurysm was weak. Western blotting results indicated that the expression level of VEGF in the aortic aneurysm was stronger than the control, while the expression level of TSP-1 was weaker than the control. Conclusion Both TSP-1 and VEGF participate in the pathogenesis of thoracic aortic aneurysm. They may be the key factors in the new vessel formation of aortic aneury