Background: It is not fully understood whether intracellular calcium and/or reactive oxygen species (ROS) are involved in nuclear factor-ĸB (NF-ĸB) activation by proinflammatory cytokines. Silymarin exhibits anti-inflammatory and antioxidant effects but the effect of silymarin in human mesangial cells is largely unknown. Method: NF-ĸB binding activity was measured by electrophoretic mobility shift assay. Intracellular calcium was monitored by confocal microscopy using Fluo-3 and intracellular ROS production was determined by flow cytometry. Monocyte chemoattractant protein-1 (MCP-1) expression was measured by Northern blot analysis and ELISA. Results: NF-ĸB was activated within 30 min by tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β). Intracellular ROS was not produced until 30 min and also antioxidants such as N-acetylcysteine and tiron had no effect on the TNF-α- or IL-1β-induced NF-ĸB activation. Intracellular calcium was increased by TNF-α and IL-1β. Furthermore, a calcium chelator, BAPTA-AM, attenuated the NF-ĸB activation. Silymarin dose-dependently inhibited the TNF-α- or IL-1β-induced NF-ĸB activation and MCP-1 expression. Silymarin also inhibited TNF-α-induced intracellular calcium. Conclusions: Induction of NF-ĸB within 30 min by TNF-α- and IL-1β was mediated through intracellular calcium but not ROS. Silymarin inhibited TNF-α-induced calcium-dependent NF-ĸB activation irrespective of its antioxidant effect.