Aim To investigate the process of neointimal formation, level of platelet activation and thrombin receptor mRNA by means of a rat aortic balloon injury model in order to study the mechanism of acute and late restenosis after percutaneous transluminal coronary angioplasty(PTCA). Methods Forty eight male Wistar rats were divided into two groups randomly. Group 1 (n=24) served as controls, group 2 (n=24) were given aortic balloon injury by self-made 2F balloon catheters. The process of intimal thickening, number of platelet GMP-140 and level of thrombin receptor mRNA were investigated at day 3, 7, 14 and 28 after balloon injury by histological method, radioimmunological method and reverse transcription polymerase chain reaction (RT-PCR) technique, respectively. Six rats were examined at each group. Results The expression of thrombin receptor mRNA was at a low level in endothelium and smooth muscle cell of normal arteries, but increased significantly at day 3 after balloon injury, reached its peak at day 14 and decreased at day 28. The number of platelet GMP-140 was higher at day 3 and began to decrease at day 7 after injury. The migration and proliferation of vascular smooth muscle cell had existed at day 3 after balloon injury. The intimal thickening began at day 7 after injury, and it was more significant at day 14. The proliferation of VSMC decreased at day 28, but extracellular matrix increased and the intimal thickening continued. Conclusions The expression of TR mRNA and the number of platelet GMP-140 increase in the process of intimal thickening after balloon injury.