To enhance the specificity of anti-TNF-α single chain Fv antibody (TNF-scFv) to inflamed site, we constructed a bispecific antibody BsDb that targets TNF-α and ED-B-containing fibronectin (B-FN) by covalently linking TNF-scFv and the anti-ED-B scFv L19 at the gene level via a flexible peptide linker deriving from human serum albumin. BsDb was successfully secreted from Pichia pastoris as functional protein, identified by immunoblotting, and purified to homogeneity with affinity chromatography. BsDb retained the immunoreactivity of its original antibodies TNF-scFv and L19, and showed a marked gain in antigen-binding affinity and in TNF-α-neutralizing ability, when compared to TNF-scFv and L19 that were produced in Escherichia coli. In the adjuvant-induced arthritis (AIA) mice model, BsDb showed selective accumulation and retention in the inflamed paws but rapid clearance from blood, resulting in high arthritic paw to blood ratios. These data indicate that BsDb is endowed with high specificity to inflamed site and low toxicity to normal tissues and holds great potential for in vivo application for the targeted therapy of RA and other chronic inflammatory diseases.