We report a method for the fabrication of ZnO nanoneedle arrays by direct microwave irradiation on the Zn sheet under O-2 and Ar atmosphere (the total pressure: 1 atm). Pure hexagonal-phase ZnO structures were grown on the Zn Substrate through this synthetic method. Dimensions of synthesized needle-like Zno structures are -500 rim in length and -50 and -100 nm in diameter at the tip and the pillar, respectively. This method needs relatively low microwave irradiation power (300 W) and a short reaction time (3 min). Also, it does not require any template or catalyst. The results of this research allow us to propose the growth mechanism of ZnO nanoneedles on the Zn substrate by direct microwave irradiation.