BACKGROUND: Hepatocellular carcinoma (HCC) is the most frequent kind of liver cancer with high morbidity and mortality rates worldwide. Altered expression of BUB1 (budding uninhibited by benzimidazole 1) gene leads to chromosome instability and aneuploidy. This study investigated the expression of BUB1 and its prognostic value as well as its correlation with immune cell infiltration and immune checkpoints in HCC. RESULTS: Using the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) databases, we found that BUB1 was up-regulated in HCC, thus prompting us to validate this observation by immunohistochemistry on 57 HCC paraffin embedded tissues from Wuxi No.2 People's Hospital. Kaplan-Meier survival analysis revealed that HCC patients with high BUB1 expression had shorter overall survival (OS) time as well as progression-free interval (PFI), and disease-specific survival (DSS) time compared to the patients with low BUB1 expression. Besides, STRING database showed that the top 10 co-expression genes were mainly involved in the regulation of cell division during the mitosis. Gene Ontology (GO) analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that BUB1 had a connection to cancer related pathways. Lastly, The Tumor Immune Estimation Resource (TIMER) analysis found that BUB1 was positively related to immune cell infiltration and some immune checkpoint gene in HCC. CLINICAL TRIAL NUMBER: Not applicable. CONCLUSIONS: Our present study demonstrated that BUB1 is a potential prognostic biomarker, and BUB1 may play a role in the tumor immune microenvironment in HCC.