Objective: To investigate the effects of hepatitis B virus (HBV) X protein (HBx) on the expression of tumor necrosis factor-α (TNF-α) in glomerular mesangial cells (GMCs) and the underlying intracellular signal pathways. Methods: The plasmid pCI-neo-X that carries the X gene of hepatitis B virus was transfected into cultured GMCs. HBx expression in the transfected GMCs was assessed by Western-blot. TNF-α protein and mRNA were assessed by ELISA and semi-quantitative RT-PCR, respectively. Three kinase inhibitors-U0126, an inhibitor of extracellular signal-regulated kinases (ERKs); lactacystin, an inhibitor of nuclear factor-κB (NF-κB); and SB203580, a selective inhibitor of p38 MAP kinase (p38 MAPK) were used to determine which intracellular signal pathways may underlie the action of HBx on TNF-α expression in transfected GMCs. Results: A significant increase in HBx expression in pCI-neo-X transfected GMCs was detected at 36 h and 48 h, which was not affected by any of those kinase inhibitors mentioned above. A similar increase in the expression of both TNF-α protein and mRNA was also observed at 36 h and 48 h, which was significantly decreased in the presence of U0126 or lactacytin, but not SB203580. Conclusions: HBx upregulates TNF-α expression in cultured GMCs, possibly through ERKs and NF-κB pathway, but not p38 MAPK pathway. © 2013 Asian Pacific Tropical Biomedical Magazine.