AMP-activated protein kinase (AMPK) is tightly regulated by the cellular AMP:ATP ratio and plays a central role in regulation of energy homeostasis and metabolic stress. Metformin has been shown to activate AMPK. We hypothesized that metformin may prevent nuclear factor κB (NF-κB) activation in endothelial cells exposed to inflammatory cytokines. Metformin was observed to activate AMPK, as well as its downstream target, phosphoacetyl coenzyme A carboxylase, in human umbilical vein endothelial cells (HUVECs). Metformin also dose-dependently inhibited tumor necrosis factor (TNF)-α–induced NF-κB activation and TNF-α–induced IκB kinase activity. Furthermore, metformin attenuated the TNF-α–induced gene expression of various proinflammatory and cell adhesion molecules, such as vascular cell adhesion molecule-1, E-selectin, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1, in HUVECs. A pharmacological activator of AMPK, 5-amino-4-imidazole carboxamide riboside (AICAR), dose-dependently inhibited TNF-α- and interleukin-1β–induced NF-κB reporter gene expression. AICAR also suppressed the TNF-α- and interleukin-1β–induced gene expression of vascular cell adhesion molecule-1, E-selectin, intercellular adhesion molecule-1, and monocyte chemoattractant protein-1 in HUVECs. The small interfering RNA for AMPKα1 attenuated metformin or AICAR–induced inhibition of NF-κB activation by TNF-α, suggesting a possible role of AMPK in the regulation of cell inflammation. In light of these findings, we suggest that metformin attenuates the cytokine-induced expression of proinflammatory and adhesion molecule genes by inhibiting NF-κB activation via AMPK activation. Thus, it might be useful to target AMPK signaling in future efforts to prevent atherogenic and inflammatory vascular disease.