Trichosanthin (TCS), isolated from the root tuber of Trichosantheskirilowii, a well-known traditional Chinese medicinal plant, belonging to the Cucurbitaceae family, was found to exhibit numerous biological and pharmacological activities including anti-inflammatory. However, the effects of TCS on arterial injury induced neointimal hyperplasia and inflammatory cell infiltration remains poorly understood. The aim of study was to examine the effectiveness of TCS on arterial injury-mediated inflammatory processes and underlying mechanisms. A balloon-injured carotid artery induced injury in vivo in rats was established as a model of vascular injury. After 1 day TCS at 20, 40, or 80 mg/kg/day was administered intraperitoneally, daily for 14 days. Subsequently, the carotid artery was excised and taken for immunohistochemical staining. Data showed that TCS significantly dose-dependently reduced balloon injury-induced neointima formation in the carotid artery model rat, accompanied by markedly decreased positive expression percentage proliferating cell nuclear antigen (PCNA). In the in vitro study vascular smooth muscle cells (VSMC) were cultured, proliferation stimulated with platelet-derived growth factor-BB (PDGF-BB) (20 ng/ml) and TCS at 1, 2, or 4 μM added. Data demonstrated that TCS inhibited proliferation and cell cycle progression of VSMC induced by PDGF-BB. Further, TCS significantly lowered mRNA expression of cyclinD1, cyclinE1, and c-fos, and protein expression levels of Akt1, Akt2, and mitogen-activated protein kinase MAPK (ERK1) signaling pathway mediated by PDGF-BB. These findings indicate that TCS inhibits vascular neointimal hyperplasia induced by vascular injury in rats by suppression of VSMC proliferation and migration, which may involve inhibition of Akt/MAPK/ERK signal pathway.