Background and Aims: Programmed cell death-1 (PD-1) plays an important role in downregulating T lymphocytes but the mechanisms are still poorly understood. This study aimed to explore the role of PD-1 in CD8+ T lymphocyte dysfunc-tion in hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF). Methods: Thirty patients with HBV-ACLF and 30 healthy controls (HCs) were recruited. The differences in the numbers and functions of CD8+ T lymphocytes, PD-1 and glucose transporter-1 (Glut1) expression from the peripheral blood of patients with HBV-ACLF and HCs were analyzed. In vitro, the CD8+ T lymphocytes from HCs were cultured (HC group) and the CD8+ T lymphocytes from ACLF patients were cultured with PD-L1-IgG (ACLF+PD-1 group) or IgG (ACLF group). The numbers and functions of CD8+ T lymphocytes, PD-1 expression, glycogen uptake capacity, and Glut1, hexokinase-2 (HK2), and pyruvate kinase (PKM2) expression were analyzed among the HC group, ACLF group and ACLF+ PD-1group. Results: The absolute numbers of CD8+ T lym-phocytes in the peripheral blood from patients with HBV-ACLF were lower than in the HCs (p<0.001). The expression of PD-1 in peripheral blood CD8+ T lymphocytes was lower in HCs than in patients with HBV-ACLF (p=0.021). Com-pared with HCs, PD-1 expression was increased (p=0.021) and Glut1 expression was decreased (p=0.016) in CD8+ T lymphocytes from the HBV-ACLF group. In vitro, glycogen uptake and functions of ACLF CD8+ T lymphocytes were sig-nificantly lower than that in HCs (p=0.017; all p<0.001). When PD-1/PD-L1 was activated, the glycogen uptake rate and expression levels of Glut1, HK2, and PKM2 showed a de-creasing trend (ACLF+PD-1 group compared to ACLF group , all p<0.05). The functions of CD8+ T lymphocytes in the ACLF+PD-1 group [using biomarkers of Ki67, CD69, IL-2, interferon-gamma, and tumor necrosis factor-alpha- were lower than in the ACLF group (all p<0.05). Conclusions: CD8+ T lymphocyte dysfunction is observed in patients with HBV-ACLF. PD-1-induced T lymphocyte dysfunction might in-volve glycolysis inhibition.