Electrically conducting materials exhibiting biological activity are desirable biomaterials as they allow for intimate interactions with cells and tissues both in electrical and biological ways. Thus, immobilization of biomolecules on conducting polymer surface is essential to produce bioactive conducting tissue scaffolds. Here, we synthesize and electrochemically polymerize carboxylic functionalized terthiophene. The produced conducting films exhibit relatively good conductivity (1.22 ± 0.15 S cm−1) and carboxylic functionality that can be used for further covalent modification with biological molecules, such as a cell adhesive peptide. We chemically immobilize fibronectin-derived Arg-Gly-Asp (RGD) peptide on the carboxylic groups on the conducting films. Our in vitro culture study with human dermal fibroblasts indicates that the GRD-grafted conducting materials support fibroblast growth and show improved cell adhesion compared to unmodified controls. Our bioactive conducting biomaterials can be applied for various biomedical applications such as bioelectrodes and tissue scaffolds.