The aryl hydrocarbon receptor (AhR) is a very unstable protein. AhR binds to the molecular chaperone complex (HSP90-p23-XAP2) to maintain a stable structure in the cytoplasm. After binding to ligands, such as dioxin, AhR translocates from the cytoplasm to the nucleus with a molecular chaperone complex. The protein forms a heterodimer with Arnt after nuclear transfer, functions as a transcription factor by binding to a xenobiotic responsive element (XRE), and induces the cytochrome P450 1A1 (CYP1A1). Because of the unstable protein, expression of the full-length AhR in the E. coli expression system is very difficult. Many studies investigated AhR using AhR domains in vitro. We expressed and purified the human full-length AhR in E. coli expression system. Furthermore, specific antibodies were prepared. Purified full-length AhR could bind to ligand. In the presence of ligand, α-helix and random coil of AhR increased and β-sheet decreased on CD spectrum. Full-length AhR could bind to HSP90, XAP2 and p23 in the presence or absence of ligand. We now show the biochemical properties of full-length AhR.