Nonlinear structures with specially designed nonlinearities, including quasi-zero stiffness, multi-stability, and frequency-up conversions, are of significant interest for energy harvesting and vibration isolation. This paper experimentally evaluates a 3-DOF (3-degrees-of-freedom) X-shaped structure coupled with a piezoelectric harvesting mechanism to enable multidirectional low-frequency energy harvesting and vibration isolation. The X-structure enables performance tunability and facilitates energy harvesting and vibration isolation in multiple directions. In multidirectional vibration experiments, the test results demonstrate the effectiveness of the 3-D X-mechanism, which exhibits robust band-pass-like harvesting spectra, enabling broadband energy harvesting at low frequencies and in multiple directions. The results indicated the capability of the 3-D X-structure, as a passive structure, to effectively achieve multidirectional vibration isolation. The X-structure demonstrated peak power outputs of 3, 0.05, and 0.065 mW under low-frequencies in the vertical, horizontal, and in-plane rotation directions, respectively. Due to the beneficial high static and low dynamic nonlinear stiffness, our X-structure achieved effective low-frequency vibration isolation (<4 Hz) more effectively in vertical and horizontal directions.