Abstract: AIM: To study the effects of granulocyte colony-stimulating factor (G-CSF) and Thy1.1 stem cell transplantation on endothelial hyperplasia, to evaluate the influence of stem cell transplantation on restenosis and to study whether G-CSF can cooperate with Thy1.1 stem cells to repair injured arteries. METHODS: One hundred twenty female Sprague Dawley (SD) rats were randomly divided into four groups (30/group): G-CSF group, stem cell transplantation group, combination transplantation group and control group. Rats in G-CSF group were injected daily with 30 μg G-CSF/kg for 7 days before carotid artery injury, rats in stem cell transplantation group were injected with 5×106 Thy1.1 stem cells (obtained from from 4- to 6-week-old male SD rats) into the injured artery after carotid artery injury, rats in combination transplantation group were injected with G-CSF and Thy1.1+ stem cells in the same manner as previously mentioned, and rats in control group were injected the same amount of saline into carotid artery. The animals were killed shortly after injury and 3, 7, 14, 21, and 28 days after balloon denudation and samples of carotid artery were harvested for pathological analysis and RT-PCR for eNOSmRNA. RESULTS: Intimal thickness was thinner in G-CSF group and stem cell transplantation group (P<0.05, P<0.01), eNOS mRNA expression was higher in G-CSF group and stem cell transplantation group compared with those in control group (P<0.05, P<0.01). Intimal thickness was lower and eNOSmRNA expression was higher in the combination transplantation group compared with those in other groups (P<0.05, P<0.01). CONCLUSION: G-CSF and stem cell transplantation accelerate reendothelialization and decrease neointimal formation following vascular injury, suggesting that stem cell transplantation may be a feasible strategy to prevent restenosis after PCI. G-CSF can cooperate with Thy1.1 stem cells to repair the injured artery.