The alteration of platelet function plays a key role in thrombosis formation. This study aimed to explore platelet function alterations in the formation of portal vein thrombosis (PVT) in cirrhosis.Cirrhotic patients admitted to hospital between October 2021 and April 2023 were recruited and divided into PVT and non-PVT groups. Flow cytometry was used to detect the expression of CD62p, CD63, monocyte-platelet aggregates (MPAs), neutrophil-platelet aggregates (NPAs) and vWF-Ag to evaluate platelet activation and adhesion function.A total of 145 subjects were enrolled in our study including 60 cirrhotic PVT patients, 60 cirrhotic non-PVT patients and 25 healthy volunteers. The expression of CD41+CD62p+ and CD41+CD63+ platelets in the PVT group was significantly elevated compared with that in the non-PVT group(P＜0.05). Subgroup analysis showed that the mean fluorescent intensity (MFI) of CD62p and CD63 was associated with portal hypertension-related complications (P＜0.05), and CD63 MFI was significantly associated with thrombosis burden (P=0.019). CD41+CD62p+ and CD41+CD63+ platelets as well as MPAs and NPAs were highly expressed in the splenectomy group (P＜0.05). Positive correlations were found between CD62p and CD63 MFI, MPAs and NPAs(P＜0.05). In addition, platelet counts were also correlated with MPAs (r=0.556, P＜0.001) and NPAs (r=0.467, P＜0.001). Cirrhotic patients with PVT had higher mortality and were more likely to experience portal hypertension-related complications (P＜0.05).Highly activated platelet function exists in patients with cirrhosis, and platelet activation was elevated during PVT formation, suggesting that activated platelets may participate in the formation of PVT in patients with cirrhosis.Thieme. All rights reserved.