Nuclear factor-κB (NF-κB) is an inducible transcription factor activated by a variety of cytokines, and promotes the transcription of genes involved in cancer, inflammation, autoimmune disease, and viral infection, among others. Because of its involvement in numerous disease processes, considerable research has focused on NF-κB as a potential drug target. We previously reported that cupric ion (Cu(2+)) blocks NF-κB activation. However, Cu(2+) is unsuitable for drug applications. The copper complex of an artificial peptide HPH-Pep (HPH-Pep-Cu(2+)) was a promising alternative, but it did not easily cross the cell membrane. We report the development of a NF-κB inhibiting Cu(2+) complex with improved cell-penetrating activity arising from the coupling of a Tat peptide to HPH-Pep-Cu(2+).