ObjectiveTo explore the inhibition action of valproic acid to inflammatory cells and smooth muscle cells then to find out that valproic acid (VPA) can repress rat thoracic aortic aneurysm or not. MethodsThe model of rat thoracic aortic aneurysm was built through the method of soaking the adventitia of artery using porcine pancreatic elastase (PPE). The rats were divided into three groups:a normal saline blank control group (a C group), an adventitia soaked PPE group (a P group), and adventitia soaked PPE plus intraperitoneal injection by injecting intraperitioneal VPA 200 mg/kg for seven days (a PV group).The animals of the three groups were all using vascular ultrasound to detect blood vessel diameter. Animals were killed after operation to observe the general morphology of vascular aneuysm and do the immunohistochemial, morphological, protein analysis of interleukin 1 (IL-1), interleukin 6 (IL-6), smooth muscle 22 alpha (SM22α), matrix metallopeptidase 2 (MMP-2), MMP-9 and Western blot by drawing animals on the 14th day. ResultsThe vessels diameter in the PV group was narrower than that in the P group (P value<0.05). HE staining, immunohistochemistry and Western blot displayed that the cells in the P group were in disorder arrangement and interstitial disorder while the cells in the PV group maintained better albumin layer. The protein expressions of IL-1, IL-6, MMP-2, and MMP-9 in the PV group decreased except that SM22α increased. ConclusionVPA can inhibit phenothpic transforming of aneurysm inflammatory cells and smooth muscle cells, reduce the levels of cell proliferation, decrease the secretion of matrix metalloproteinases, and depress tumor growth of rat thoracic aorta.