The interactions between an electrochemically fabricated Ag quantum wire and NH3 molecules in an aqueous environment were studied. The Ag quantum wire showed a stepwise decrease of conductance change upon exposure to the definite concentration of NH3 molecules in an aqueous environment. Similar changes were also observed when an Ag quantum wire interacted with methyl amine, ethylenediamine and acetonitrile molecules, respectively. We experimentally probed the mechanism for the conductance modulation in the case of ammonia and proposed a model to describe it. The Ag quantum wire showed a conductance increasing process upon addition of the chemical reduced regent, sodium borohydride or ascorbic acid. Conductance increase was also seen with a process of electrochemical reduction. Based on the related data, we further proposed the existing partly Ag ions in the Ag quantum wire surface played a key role for these changes of Ag wire conductance. The work also showed the unique property of atomic-scale metal electrode different from the bulk electrode. (C) 2012 Elsevier Ltd. All rights reserved.