The Toll-like receptor (TLR) family has important roles in microbial recognition and dendritic cell activation^,. TLRs 7 and 9 can recognize nucleic acids^,,, and trigger signalling cascades that activate plasmacytoid dendritic cells to produce interferon-α (IFN-α) (refs , ). TLR7/9-mediated dendritic cell activation is critical for antiviral immunity but also contributes to the pathogenesis of systemic lupus erythematosus, a disease in which serum IFN-α levels are elevated owing to plasmacytoid dendritic cell activation^,. TLR7/9-induced IFN-α induction depends on a molecular complex that contains a TLR adaptor, MyD88, and IFN regulatory factor 7 (IRF-7) (refs ), but the underlying molecular mechanisms are as yet unknown. Here we show that IκB kinase-α (IKK-α) is critically involved in TLR7/9-induced IFN-α production. TLR7/9-induced IFN-α production was severely impaired in IKK-α-deficient plasmacytoid dendritic cells, whereas inflammatory cytokine induction was decreased but still occurred. Kinase-deficient IKK-α inhibited the ability of MyD88 to activate the Ifna promoter in synergy with IRF-7. Furthermore, IKK-α associated with and phosphorylated IRF-7. Our results identify a role for IKK-α in TLR7/9 signalling, and highlight IKK-α as a potential target for manipulating TLR-induced IFN-α production.