Hepatocellular carcinoma (HCC) is a malignant tumor that has become a global health issue. The aim of the present study was to examine the role of transmembrane protein 9 (TMEM9) in cell progression, such as cell growth, cell cycle, cell metastasis of hepatoma cells, and to discuss the TMEM9 gene‑encoding protein as a potential therapy target of hepatoma. RT-qPCR was performed to examine TMEM9 expression in tumor tissues and adjacent tissues of patients with liver cancer. siRNAs were used to interfere TMEM9 in HepG2 and 7721 cells. A CCK-8 assay was performed to evaluate cell growth at 24, 48 and 72 h. Cell cycle and apoptosis were analyzed using flow cytometry. Transwell assays were used to determine cell invasion, migration and adhesion. The results showed that TMEM9 was expressed abnormally in liver cancers. TMEM9 expression increased significantly in the 34 examined patients. TMEM9 knockdown inhibited proliferation in the HepG2 and 7721 cells. The flow cytometric analysis revealed that TMEM9 knockdown by RNA interference resulted in G1 arrest and induced apoptosis. Cell invasion, migration and adhesion ability were also decreased. Western blotting indicated that expression of the cell cycle‑related proteins CDK1, EIF3H, RPL10L, S100A10, CCNB1 and CCNB2 was significantly decreased. In conclusion, TMEM9 plays an important role in the cell growth of hepatoma cells.