SMAD3, also known as mothers against decapentaplegic homolog 3, belongs to the SMAD family of proteins that mediate signal transduction by the TGF-beta/activin/BMP-2/4 cytokine superfamily from receptor Ser/Thr protein kinases at the cell surface to the nucleus. Small moleucule inhibitors of Smad3 may have tremendous clinical potential in the treatment of pathological fibrotic diseases. Recombinant SMAD3 protein was expressed in E.coli and purified by using conventional chromatography techniques.