Aim To investigate the special pharmacological effect of phenytoin on the healing process after ballon injury in rat carotid artery.Methods Study was performed on rat model of balloon-injury in common carotid artery.Rats survived from successful operation were divided into phenytoin group and injury group.On the 28th day after operation,rats were anesthetized,then the left carotids and the corresponding part of the right carotids were separated,embedded with paraffin,sectioned into 5 μm and stained.Results On the 28th day after operation,the intima area(0.154±0.018 mm2 vs 0.204±0.054 mm2,p<0.01),intima/media area(1.70±0.08 vs 2.26±0.46,p<0.01)and the rate of restenosis(59.5%±3.2% vs 75.9%±13.3%,p<0.01)in phenytoin group were all less than those in injury group,while lumen area(0.106±0.024 mm2 vs 0.063±0.034 mm2,p<0.01)was larger than that in injury group,cell density in intima(72.18±20.08/cm2 vs 84.85±10.77/cm2,p<0.05),proliferating cell nuclear antigen(PCNA)positive cell counting(9.89±7.63 per 200 magnification vs 23.03±13.95 per 200 magnification,p<0.01)and α-smooth muscle actin positive cell counting(30.91±20.05 per 200 magnification vs 61.81±16.57 per 200 magnification,p<0.01)were all smaller than those in injury group;under polarized light,collagen could be visualized deposite in intima,but there were no statistic difference in collagen area and density(p>0.05).Conclusion 28 days after vascular injury,phenytoin can decrease the cell number in neointima and promote the synthesis of extracellular matrix which result in diminished neointima thickening.