Objective  To investigate the role of MLLT1 in hepatocellular carcinoma （HCC）and its impact on the tumor immune microenvironment.    Methods  Multivariate Cox regression analysis and tumor gene analysis tools such as GEPIA and UALCAN were used to explore the expression of the MLLT1 gene and its prognostic significance in different tumors. Real-time PCR, Western blotting, and immunohistochemistry were used to investigate the differential expression of MLLT1 between HCC tumor tissue and normal tissue. MTT assay and cell cycle analysis were performed to assess the effect of MLLT1 knockdown on cell proliferation and cell cycle. The correlation between MLLT1 and immune cells, as well as immune infiltrates in the tumor microenvironment, and their correlation with immune neoantigens, immune checkpoints, tumor mutation burden, and microsatellite instability were also explored.    Results  The MLLT1 gene was found to be aberrantly expressed in various solid tumors including HCC, and its high expression was associated with poor prognosis in HCC. Knockdown of MLLT1 inhibited HCC cell proliferation and blocked the cell cycle. High expression of MLLT1 was found to affect the content of multiple immune cells, including CD4+T cells and neutrophile granulocyte cells in the HCC microenvironment.    Conclusion  MLLT1 is highly expressed in HCC and knockdown of MLLT1 can inhibit HCC cell proliferation and block the cell cycle. MLLT1 has a certain degree of impact on the immune microenvironment of HCC. Therefore, MLLT1 may serve as a potential diagnostic biomarker and therapeutic target for HCC.