Hypoxia, a condition of low oxygen tension, occurring in many pathological processes, modifies the mononuclear phagocyte transcriptional profile. Here, we demonstrate hypoxic up-regulation of the CCL20 chemokine in primary human monocytes (Mn) and macrophages. mRNA induction was paralleled by protein secretion and dependent on gene transcription activation. Functional studies of the CCL20 promoter using a series of 5′-deleted and mutated reporter constructs demonstrated the requirement for the NF-κB-binding site located at position –92/–82 for gene transactivation by hypoxia, as 1) transcription was abrogated by a 3-bp mutation of the NF-κB motif; 2) three copies of the wild-type NF-κB-binding site conferred hypoxia responsiveness to a minimal heterologous promoter; and 3) hypoxia increased specific NF-κB binding to this sequence. Furthermore, we provide evidence of the specific role of a single NF-κB family member, p50, in mediating CCL20 gene transcription in hypoxic Mn. p50 homodimers were the only detectable NF-κB complexes binding the cognate κB site on the CCL20 promoter upon hypoxia exposure, and NF-κBp50 knockdown by lentiviral-mediated short hairpin RNA interference resulted in complete binding inhibition. NF-κBp50 overexpression in transient cotransfection studies promoted CCL20 gene transactivation, which was abrogated by mutation of the –92/–82 κB site. Moreover, nuclear expression of the other NF-κB family members was inhibited in hypoxic Mn. In conclusion, this study characterizes a previously unrecognized role for hypoxia as a transcriptional inducer of CCL20 in human mononuclear phagocytes and highlights the importance of the NF-κB pathway in mediating this response, with potential implications for inflammatory disease and cancer pathogenesis.