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Ubiquitin-specific peptidase 18 (USP18) is closely related with hepatitis B virus (HBV), which has been involved in tumourigenesis. However, there has been little research into the role of USP18 on the progression of hepatocellular carcinoma (HCC), especially in HBV-related HCC. In present study, we found that USP18 expression was aberrantly elevated in HCC tissues than adjacent non-tumour tissues. Importantly, USP18 expression was higher in HBV-related HCC cell lines (HepG2.2.15 and Hep3B) than HBV-unrelated HCC cell lines. Furthermore, knockdown of USP18 significantly suppressed tumour cell proliferation in vitro and tumour growth in vivo, whereas overexpression of USP18 promoted HCC cells growth. Moreover, our experimental data revealed that USP18 silencing obviously blocked cell cycle at G1 phase and increased cell apoptosis. Finally, BCL2L1, a member of BCL2 family protein, was identified as a downstream gene of USP18. Mechanistically, we found that USP18 directly bind to BCL2L1 and positively regulated its expression in HCC cells. Overall, our results suggested that USP18 has a crucial role in regulating diverse aspects of the pathogenesis of HCC, indicating that it might be a potential therapeutic target.