[en] Highlights: • Single-crystal PMN-PT nanobelt arrays have been obtained through a versatile top-down method. • The PMN-PT nanobelts feature the highest reported piezoelectric coefficient (~677 pm/V). • The maximum output voltage and current of the PMN-PT-based nanogenerator are ~6.0 V and ~102 μA, respectively. Microelectromechanical systems (MEMS) incorporating piezoelectric elements enable highly sensitive sensors/actuators and effective energy harvesting. The development of a facile method for fabricating high-quality, deterministically positioned piezoelectric nanostructures provides new opportunities to build MEMS devices with dramatically higher performance. Piezoelectric materials with superior piezoelectric response, such as the relaxor ferroelectric Pb(Mg,Nb)O₃-PbTiO₃ (PMN-PT) represents a particularly interesting active material that functions as sensors/actuators and energy harvesters. Bottom-up synthesis of PMN-PT nanostructure suffers from polycrystallinity and stoichiometric deficiency. Yet, another main challenge is the deterministic positioning, aligning and integrating of as-synthesized nanostructures into functional arrays, in a similar manner to top-down strategies. Here, we fabricated scalable ordered single crystalline PMN-PT nanobelt (NB) arrays via a versatile top-down method. These NBs arrays, selectively sculpted from a single crystal bulk preserve well ferroelectric properties and exhibit the highest reported piezoelectric coefficient (~677 pm/V). A flexible PMN-PT NB harvester was demonstrated based on these single crystalline NBs. The maximum output voltage and current reach ~6.0 V and ~102 μA, respectively under a 0.2% strain agitation. The result paves the way towards real application for top-down fabricated PMN-PT NBs as nanogenerators.