In this paper, we demonstrate a novel robust miniature three-axis vibrational energy-harvester using a mechanical-piezoelectric configuration. Using the configuration, the harvester employs Newton's law of inertia and the piezoelectric effect to convert either the x -axis or y -axis in-plane and z -axis out-of-plane ambient vibrations into piezoelectric voltage-responses. Under the x -axis vibration (sine-wave, 75 Hz, 3.5 g), our modeled, finite-element analyzed/simulated, and experimental root mean square voltage-response with power-outputs of the harvester (stimulated in resonant with the optimum load) is 525.36 mV with 0.477 μW , 516.51 mV with 0.461 μW , and 548 mV with 0.519 μW , respectively. Under the z -axis vibration (sine-wave, 95 Hz, 3.8 g), the modeled, finite-element analyzed/simulated, and experimental root mean square voltage-response with power-output of the harvester (stimulated in resonant with the optimum load) is 157.35 mV with 0.066 μW , 170.25 mV with 0.0772 μW , and 168 mV with 0.075 μW , respectively. These show that not only both of our modeling and finite-element analysis/simulation can successfully predict the experimental results, but also our harvester is capable of harnessing three-axial ambient vibrations. Moreover, through the piezoelectric lead-zirconate-titanate-connected-in-series approach, the voltage and power outputs are increased. According to these achievements, we believe that our harvester would be an important design reference in industry for future development of microfabrication-based (MEMS-based) three-axial piezoelectric energy harvesters and accelerometers.