Hsp90 (90 kDa heat shock protein) is a molecular chaperon involved in protein folding and regulating the stability and activation state of many client proteins under stress and normal conditions. Hsp90 is an attractive target for the therapeutics against cancer and virus infectious diseases. Hsp90 undergoes large conformational changes during its functional cycle driven by ATP binding and hydrolysis to ADP at the N-terminal domain. ATP-binding and ADP-dissociation play key roles for the functions of Hsp90. All-atom molecular dynamics simulations of the N-terminal domain of human Hsp90 in complex with ADP are carried out to elucidate the dissociation process of ADP at atomic resolution. The MD simulations with the binding-distance constraint are performed. Our results show that ADP is dissociated from the binding pocket of Hsp90 with Mg2+, and that ADP has two possible conformation and two possible pathways in the dissociation process. © 2012 Wiley Periodicals, Inc.