Signal transducer and activator of transcription 4 (STAT4) is a transcription factor in the JAK/STAT signaling pathway that is activated by interleukins and plays a critical role in the differentiation of T-helper 1 cells. The STAT4 luciferase reporter vector is designed to study the transcriptional activity of STAT4. The vector contains a STAT4 DNA consensus binding site and TA minimal promoter upstream of a firefly luciferase reporter gene, which can specifically report STAT4 activity while maintaining a low basal level of transcription.