We describe the trapping characteristic of hyaluronic acid (HA) molecules using silicon micromachined nanotweezers having two opposed needle tips ( gap) that were coated with Al, Au, and Pt thin films. In an aqueous HA solution, ac voltage (, sine wave) was applied between the nanotweezer tips. In the experiments using the Al-coated nanotweezers, HA molecules were successfully trapped as a thin string bridged between the tips of the nanotweezers when the frequency of applied ac voltage was or higher. The diameter of the trapped string tended to decrease when the frequency of the applied ac voltage was increased. A molecular string with a diameter of consisting of a bundle of multiple HA molecules was obtained when the frequency of the applied ac voltage was . In addition to the Al-coated nanotweezers, HA molecules were also successfully trapped as a string using the nanotweezers with tips coated with Au and Pt thin films.