Objective-Inflammation is one of the main pathogeneses of neointimal hyperplasia after coronary intervention.Thalidomide, because of its potent antiinflammatory and immunomodulatory properties, is being re-evaluated in several clinical fields. Therefore, we examined whether thalidomide therapy affects neointimal formation. Methods and Results-In male Sprague-Dawley rats, 100 mg/kg of either thalidomide or sucrose (control) was administered daily from 3 days before injury to 2 weeks after conventional carotid artery denudation injury. Thalidomide administration resulted in a significant reduction of neointimal formation (neointima to media ratio 1.26Ϯ0.29 versus 0.35Ϯ0.13, PϽ0.001) and proliferative activity of vascular smooth muscle cells. In addition, arterial macrophage infiltration and local expressions of tumor necrosis factor alpha (TNF-␣) and basic fibroblast growth factor (bFGF) in the injured arteries as measured by immunohistochemistry and immunoblot analysis were significantly reduced by thalidomide treatment. Serum TNF-␣, measured by ELISA, was also significantly reduced in the thalidomide-treated animals compared with controls after injury (856Ϯ213 versus 449Ϯ68 pg/mL on day 3, Pϭ0.001; 129Ϯ34 versus 63Ϯ18 pg/mL on day 14, Pϭ0.001), and we observed a good positive correlation between the serum TNF-␣ levels and the severity of neointimal growth. Conclusions-We found that thalidomide, through its antiinflammatory and antiproliferative effects, significantly inhibits neointimal hyperplasia in balloon-injured rat carotid arteries. Our results suggest a potential role of thalidomide as a potent inhibitor of neointimal formation after angioplasty.