BACKGROUND: Hepatocellular carcinoma (HCC) represents a significant global health challenge with high incidence and mortality rates. T cells and natural killer (NK) cells are pivotal in this context, yet HCC can evade immune surveillance. CD161 (KLRB1), a C-type lectin receptor, modulates immune responses and is expressed on NK cells and a subset of T cells. Its relevance in HCC remains poorly understood, with conflicting findings regarding its impact on patient prognosis. METHODS: Utilizing TCGA data and single-cell analysis, we investigated the biological functions of KLRB1 in HCC. Peripheral blood samples from 126 HCC patients were collected to assess KLRB1 expression on NK and T cells. The diagnostic performance of KLRB1 on NK and CD8 + T cells was evaluated using receiver operating characteristic curve (ROC) analysis, while its prognostic significance was assessed using Kaplan-Meier analysis and COX regression models. RESULTS: Analysis of TCGA data revealed a significant correlation between KLRB1 expression and immune activation, particularly T cell activation. Single-cell data further demonstrated elevated KLRB1 expression in tissue-resident NK and T cells within HCC, which co-expressed markers of immune activation. Clinical data showed downregulated KLRB1 expression on NK and T cells in HCC patients compared to health individuals, with lower expression levels correlating with poorer prognosis. CONCLUSION: KLRB1 emerges as a promising biomarker in HCC, with its downregulation on peripheral blood NK and T cells suggesting potential prognostic value. Further elucidation of KLRB1's role in HCC may pave the way for the development of targeted immunotherapies and the improvement of patient outcomes.