Pyrrole-imidazole (Py-Im) polyamides can bind to the predetermined base pairs in the minor groove of double-helical DNA with high affinity. These synthetic small molecules can interfere with transcription factor-DNA interaction and inhibit or activate the transcription of corresponding genes. In the present study, we designed and synthesized a Py-Im polyamide to target -545 to -539 base pairs of human transforming growth factor- beta 1 (hTGF-beta 1) promoter adjacent to the fat-specific element 2 (FSE2) to inhibit the expression of the gene. Gel mobility shift assay showed that the synthetic Py-Im polyamide binds to its corresponding double-strand oligonucleotides, whereas the mismatch polyamides did not bind. Fluorescein isothiocyanatelabeled Py-Im polyamide was detected in the nuclei of human vascular smooth muscle cells (VSMCs) after 2- to 48-h incubation. Py-Im polyamide significantly decreased the promoter activity of hTGF-beta 1 determined by in vitro transcription experiments and luciferase assay. In cultured human VSMCs, Py-Im polyamide targeting hTGF-beta 1 promoter significantly inhibited expressions of hTGF-beta 1 mRNA and protein. These results indicate that the synthetic Py-Im polyamide designed to bind hTGF-beta 1 promoter inhibited hTGF-beta 1 gene and protein expression successfully. This novel agent will be used for the TGF-beta-related diseases as a gene therapy.