Rifamycin belong to the family of benzoquinone ansamycin of which most of them with drugable activity,e.g.geldanamycin is one of the known inhibitor of Hsp90.As a promising target in cancer therapy,the molecular chaperone Hsp90 (heat shock protein 90) is more and more concerned about in recently research.Thinking of the structure activity relationship of rifamycin with the known inhibitor geldanamycin of Hsp90 which inspire us to research the affinity of rifamycin with Hsp90 by the normal method of spectroscopic and molecular docking.And the result show that rifamycin maybe a potential agonist for the protein of Hsp90 owing to the high affinity with Hsp90 and weak inhibition for ATPase of Hsp90,using fluorescence quenching method and the ATPase analysis system(Fig.1).The associat constant is about 106-7 M-1 that be in the binding constant range of the most ligand and receptor.The positive △H0 and △S0 are-21.8±2.30 KJ/mol,60.5±3.87 J/mol respectively which indicated that electrostatic force play an important role in the rifamycin bind to Hsp90,and the associate constant K 8.5±1.93 × 106M-1,5.3±0.24× 106M-1,4.6±0.26× 106 M-1 at 293K,303K,310K respectively.The conformational changes in Hsp90,which also confirmed by CD or UV-Vis spectra.The CD spectrum presented that the second structure changed of Hsp90 by the binding of rifamycin.Further,molecular docking model predict the binding complex between Hsp90 and rifamycin,which also support the fluorescent spectropic results.