Nanostructure engineering has been extensively applied to ZnO in an effort to improve its performance in thermoelectric material, solar cell, and nanogenerator applications. Nano-structured ZnO bulks are limited by their inherently low mobility caused by the high density of grain boundaries and interfaces. In this study, a hybrid micro/nano structure composed of nearly coherent grain boundaries with a low misorientation degree among the nanograins was successfully fabricated in Zn 1− x Al x O ( x = 0, 0.01, 0.02, 0.03, 0.04 mol) bulks via hydrothermal synthesis and spark plasma sintering. Despite the large amount of nanograin boundaries and interfaces in the resulting material, a high carrier mobility value (50.7 cm 2 V −1 s −1 ) was obtained in the x = 0.2 sample - close to the level shown by ZnO single crystals and far higher than that of its ordinary nano-structured counterparts (<15 cm 2 V −1 s −1 ). A reduced thermal conductivity value of 2.1 W m −1 K −1 at 1073 K was also obtained in the micro/nano-structured x = 0.02 bulk due to extremely effective scattering at boundaries and interfaces also present in the nano-structured counterparts. After the simultaneous optimization of both electrical and thermal transport properties, the micro/nano-structured x = 0.02 sample showed a high ZT value (up to 0.36) at 1073 K. The proposed micro/nano-structure may also be applicable to other thermoelectric materials for further ZT enhancement. We obtained a high thermoelectric figure of merit ( ZT ) in this simple ZnO by adopting a hybrid micro/nano structuring approach.