Hepatocellular carcinoma (HCC) is one of the most commonly diagnosed malignancy globally with a pessimistic prognosis. Previous studies have demonstrated that abnormal expression of genes in the lysine-specific histone demethylase 3 (KDM3) family with epigenetic changes and dysregulation of enzymes promotes cancer progression. In this study, multiomics analyses were utilized to analyze differential expression, prognostic value, genetic alteration, protein–protein interaction, associated biological pathways and immune cell infiltration of KDM3s in patients with HCC. KDM3A-C were significantly upregulated to different extents based on pathologic and tumor grades in patients with HCC compared to normal tissue. Of note, higher KDM3A expression was associated with poor survival in HCC patients, whereas KDM3B and KDM3C were not associated with survival. Furthermore, KDM3A-B genetic alterations had significant effects on survival in patients with HCC. Analyses of the KEGG pathway and miRNAs targets of KDM3A and KDM3B in HCC may provide potential value in tumor behaviors and treatment. The differential expression of the KDM3 family has a strongly significant correlation with the infiltration of the abundance of immune cells, including B cells, CD8⁺ T cells, CD4⁺ T cells, macrophages, neutrophils, and dendritic cells in HCC. This study indicates that KDM3A may have the potential to be a promising molecular target in terms of prognostic biomarkers or therapeutic targets for HCC treatment.