The tunable single-degree-of-freedom rotational energy harvester is proposed. The device is the combination of the rotational energy harvester and the suspended weight. Thus, it can harvest the electrical power from the translational base excitation associated with low frequency and large amplitude. Further, its natural frequency can be changeable by manipulating the size of the reel (i.e., geometrical tunability). The characteristics of the proposed device are investigated through numerical simulation and experimental test. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3644130]