Background: Previously, we have demonstrated that HMC05, a water extract from 8 medicinal herbs, has anti-inflammatory effects in murine macrophages and anti-atherosclerotic effects in ApoE-/- mice. One notable finding was the preservation of the smooth muscle cell(SMC) layer by HMC05 in the media of aorta of high-fat high-cholesterol fed mice. Hsp27 expression was shown to be decreased in the advanced atherosclerotic plaque of human caroitid arteries. In the present study, we have investigated whether HMC05 and HMC05 fractions, a single compound derived from HMC05, can affect restenosis using balloon injury model in rats and decrease SMC migration in scratch model in culture dish. Also we tried to investigate the role of Hsp27 in the inhibition of neointima formation. Results: To induce neointima formation, the right carotid artery of Male SD rats (400~450g) was exposed, inserted with a 2F Fogarty catheter in an defined arterial segment, and then the endothelium was denuded by moving the catheter back and forth 3-4 times. HMC05 (160mg/kg/day) was administered by tube feeding starting from 4days before surgery and continued for 2 weeks after carotid injury. Injured carotid arteries isolated from rats were embedded in paraffin block and tissue sections were stained with H&E to assess neointima formation. Although there was no significant difference in medial area between control and treated group (Control: 0.93mm2, HMC05: 0.92mm2), intima to media ratios was 37.25-fold lower in rats treated HMC05 than in control. Immunohistochemistry and confocal analysis confirmed that medial SMCs of arterial wall from rats treated with HMC05 showed significant overexpression of HSP27 compared with that of control rats. In addition, cell migration/proliferation was dramatically inhibited when RVSMCs were treated with HMC05 or HMC05 fraction in the scratch model in culture dish. Conclusions: HMC05 showed significant inhibition of neointima formation in rat carotid artery balloon injury model. Increased expression of Hsp27 in the medial SMCs were noted in HMCO5 treated rats. When RVSMCs were treated with HMC05 or HMC05 fraction in the scratch in culture SMC migration and proliferation was inhibitied.