Background <p>Hepatocellular carcinoma (HCC) is the sixth most diagnosed cancer worldwide and the third leading cause of cancer-related mortality. Recently, considerable advancements have been made in cancer treatment due to immunotherapy. However, the role of acarbose (ACA), a widely used antidiabetic medication, in HCC remains largely unexplored, limiting its clinical application alongside immunotherapy.</p> Methods <p>We conducted various in vivo and in vitro experiments, including cell counting kit-8, colony formation, and wound-healing assays, to evaluate ACA’s effects on HCC cell proliferation, migration, and colony formation. Additionally, bioinformatics analysis and quantitative real-time polymerase chain reaction (qPCR) were employed to assess maltase–glucoamylase (MGAM) expression levels. Furthermore, cell transfection and qPCR were performed to investigate the antitumor mechanisms associated with ACA. Immunohistochemical staining was used to analyze CD8⁺ T cell infiltration within tumor tissue, and a subcutaneous tumor model was developed to assess potential enhanced effects with anti-programmed death 1 (anti-PD-1) and anti-cytotoxic T-lymphocyte-associated antigen 4 (anti-CTLA-4) therapies.</p> Results <p>ACA inhibited HCC cell proliferation, colony formation, and migration in both in vitro and in vivo settings. Notably, ACA enhanced CD8⁺ T cell infiltration and improved the efficacy of anti-PD-1 and anti-CTLA-4 treatments. Mechanistically, our findings suggest that ACA impede HCC progression and potentially mediated by downregulating MGAM expression.</p> Conclusions <p>Our preclinical study indicates that ACA attenuates aggressive biological behaviors of HCC cells and improves the efficacy of immune checkpoint inhibitors, including anti-PD-1 and anti-CTLA-4 therapies. These observations offer a preclinical rationale for exploring combinations of ACA with anti-PD-1 or anti-CTLA-4 therapies for HCC in future investigations.</p>