Introduction. Transmembrane protein 65 (TMEM65) is an inner mitochondrial membrane protein, which played important role in mediating autophagy, smooth muscle contraction, protein glycosylation, and immune response. In recent years, the interest had risen for exploring the function of the TMEM genes in the cancer fields. As a consequence, in our pan-cancer research of the TMEM65, we explored the function of the gene in kinds of database and tried to apply the finding in the clinical practice. Methods. In this research, we provide a comprehensive investigation of TMEM65 expression in a pan-cancer manner containing 33 cancer types. We evaluated the association of TMEM65 with the prognosis, immune infiltration, drug sensitivity analysis, GSVA enrichment analysis, TMB, MSI, NEO, and hotspot mechanisms. Results. TMEM65 was abnormally expressed in 24 types of cancers and showed correlation with the OS for 6 cancers and PFI for 9 cancers and kpI for 3 types. Moreover, the TME score, CD8 T effector, and immune checkpoint scoring systems showed a close correlation with the TMEM65. Moreover, TMEM65 was strongly correlated with some of the most common tumor-related genes and certain pathways (TGF beta signaling, TNFA signaling, hypoxia, pyroptosis, DNA repairing, autophagy, ferroptosis, and other related genes). Additionally, the TMEM65 showed correlations with the tumor mutational burden (TMB), microsatellite instability (MSI), NEO, and drug sensitivity. Finally, we confirmed several pathways by the GSEA and GSVA for the TMEM65 at the breast cancer aspects. Nomogram prediction model was also established for the breast tumors based on the TMEM65 level and other variables. Conclusion. Above all, the TMEM65 played important roles in predicting the prognosis of the cancers and correlated with the tumor immunity in the pan-cancer analysis.