Abstract: Objective To investigate the role and the mechanism of reactive oxygen species (ROS) in PSL-induced GP Ibα ectodomain shedding. Methods We took apheresis-derived platelet from healthy volunteers, concussed at 22℃, saved a certain amount of platelets with a sterile tubing machine at 1, 3 and 5 days, respectively. We used flow cytometry to detect cell ROS, mitochondrial membrane potential depolarization, phosphatidylserine (PS) eversion and P-selectin expression. We detected the glycocalicin (GC), a soluble N-terminal fragment of GPIbα that is released during ectodomain shedding. We used western blot to test p38 mitogen-activated protein kinase (MAPK) phosphorylation. Results With the extension of storage time, platelet activation and apoptosis occurred gradually, p38 MAPK phosphorylation gradually increased, the content of GC in plasma gradually increased, ROS antagonist inhibited platelet intracellular ROS, and the phosphorylation of p38 MAPK, the content of plasma GC was reduced. P38 MAPK inhibitor inhibited p38 MAPK phosphorylation and reduced the content of GC in plasma, and did not inhibit ROS concentration. Conclusion ROS plays an important role in the PSL-induced GPIbα ectodomain shedding, and ROS may thereby cause GP Ibα ectodomain shedding by activating p38 MAPK.