Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the toxic and biological effects of a variety of chemicals. Although a significant amount of information is available with respect to the planar aromatic hydrocarbon AhR ligands, information on the actual spectrum of chemical structures that can bind to and activate the AhR is insufficient. In order to determine the binding affinities of chemicals to the human AhR (hAhR), we constructed an electrochemical system which carries the hAhR ligand-binding domain on the electrode surface. The recombinant hAhR ligand-binding domain that was expressed in Escherichia coli using a T7 expression system was immobilized on a gold electrode. The specificity of this biosensor based on a ligand-receptor interaction was comparable to other in vitro screening methods. The receptor-modified electrode can rapidly detect the binding of ligands to hAhR. The electrochemical measurement can be carried out within just 5 min. This electrochemical screening system is rapid, low in cost, and adaptable to high-throughput applications without sacrificing either sensitivity or selectivity.