Abstract: AIM This study aimed to investigate the influence of platelet glycoprotein IIb/IIIa inhibitor (GPI) tirofiban hydrochloride on endothelial function of ST segment elevation myocardial infarction (STEMI) patients. METHODS 100 STEMI patients who underwent emergency PCI in our hospitial were divided into the experimental drug group (n=73) and control group (n=27) according to whether tirofiban hydrochloride was used before PCI. Endothelial microparticle (EMP) expression was determined with cytometric bead array, whereas intercellular cell adhesion molecule-1 (ICAM-1) and endothelin-1 (ET-1) with ELISA before and after PCI in both groups. RESULTS 1) There was no significant difference of EMP, ICAM-1 and ET-1 levels in the drug experimental group and the control group before PCI. 2) There was no statistically significant difference of EMP, ICAM-1 and ET-1 levels in the drug experimental group before and after PCI. EMP level after PCI in the control group was higher than that before PCI, with statistical difference (P<0.05). ICAM-1 and ET-1 levels after PCI in the control group were significantly higher than those before PCI (P<0.01). CONCLUSION Tirofiban hydrochloride was able to inhibit the increase of EMP, ICAM-1 and ET-1 in the serum of STEMI patients after PCI, which was related to improvement of endothelial function.