Piezoelectric energy harvester converts low-frequency vibrational energy in the environment into electrical energy, enabling the purpose of self-supplying power for low-energy consumption devices. The key to miniaturizing energy harvester is the buildup of the submicron-grained ceramic with a high transduction coefficient (dxg), which is still a big challenge from a technical point of view. In this work, the popular ternary system of Pb(Zn1/3Nb2/3)O-3-Pb(Zr0.5Ti0.5)O-3 (PZN-PZT) has been selected as objective compound, and the submicron-grained ceramics were prepared by a combination of high-energy ball milling and pressureless sintering technology. The results revealed that nanocrystalline PZN-PZT powders can be synthesized by one step mechanochemical route without the calcination stage. Using these nanopowders as precursors, dense ceramics with different grain size have been prepared through tailoring the sintering temperature. The study of size-dependent energy harvesting characteristic evidenced an optimum transduction coefficient of 7980x10(-15) m(2)/N was obtained for 950 degrees C sintered specimen, which has uniform microstructure with mean grain size of 0.33 mu m. In the mode of the cantilever-type energy harvester constructed by this material, the output power at low frequency of 89 Hz was as high as 69 mu W at an acceleration of 10 m/s(2), showing the suitability for piezoelectric generators harvesting environmental vibrational energy.