Harvesting energy from ambient vibrations via piezoelectric effect has been considered as a promising solution for implementing self-sustained low-power electronic devices. Most of the proposed piezoelectric energy harvesters (PEHs) are focused on the energy harvesting from uni-directional vibration. This is a strong limitation because the vibration may come from various directions in practical applications. To address this issue, this paper presents a design and experimental verification of a compact bi-directional nonlinear PEH that is sensitive to two orthogonal directions. This nonlinear PEH is composed of two magnetically coupled piezoelectric cantilever beams with orthogonal directions of deflection. Theoretical analysis and experiments reveal that the proposed PEH can not only harvest vibration energy from various directions but also provide an enhanced output voltage as compared to its linear counterpart. The introduction of magnetic coupling also enables the energy transfer between the two beams, which helps to restrain the excessive deflection of the two beams. Moreover, the advantage of nonlinear PEH is found to be highlighted at low-level excitation, whereas the resonant frequency of the nonlinear PEH drops as the excitation level reduces. (C) 2014 Elsevier Ltd. All rights reserved.