DNA decoys have been developed for the inhibition of transcriptional regulation of gene expression. However, the present methodology lacks the spatial and temporal control of gene expression that is commonly found in nature. Here, we report the application of photoremovable protecting groups on nucleobases of nuclear factor κB (NF-κB) DNA decoys to regulate NF-κB-driven transcription of secreted alkaline phosphatase using light as an external control element. The NF-κB family of proteins is comprised of important eukaryotic transcription factors that regulate a wide range of cellular processes and are involved in immune response, development, cellular growth, and cell death. Several diseases, including cancer, arthritis, chronic inflammation, asthma, neurodegenerative diseases, and heart disease, have been linked to constitutively active NF-κB. Through the direct incorporation of caging groups into an NF-κB decoy, we were able to disrupt DNA:DNA hybridization and inhibit the binding of the transcription factor to the DNA decoy until UV irradiation removed the caging groups and restored the activity of the oligonucleotide. Excellent light-switching behavior of transcriptional regulation was observed. This is the first example of a caged DNA decoy for the photochemical regulation of gene expression in mammalian cells and represents an important addition to the toolbox of light-controlled gene regulatory agents.