Herein, we present the growth of pristine vertically aligned flexible two dimensional (2D) pure ZnO nanodiscs via a simple seed assisted solution route and their use in the fabrication of a piezoelectric nanogenerator. The preferred growth direction and morphology of wurtzite ZnO nanodiscs were investigated using X-ray diffraction and field emission scanning electron microscopy (FESEM) studies. A flexible piezoelectric nanogenerator was fabricated using the vertically aligned ZnO nanodiscs as the active piezoelectric material and a carbon nanotube–polydimethylsiloxane (CNT : PDMS) film as the top electrode. This unique 2D-type ZnO nanodisc-based nanogenerator generated a direct current (DC) type output voltage and current density of about 2.5 V and 30 nA cm⁻² under compressive vertical strain, respectively. Significant enhancement of the piezoelectric output voltage from the flexible nanogenerator based on the vertically aligned two dimensional (2D) zinc oxide (ZnO) nanodiscs was achieved via thermal annealing. An output voltage and current density of 17 V and 150 nA cm⁻² were detected from the thermally annealed 2D ZnO nanodisc based nanogenerator which is approximately 8 times higher (voltage) than that from the pristine nanogenerator. It is proposed that the output performance of the vertically aligned ZnO nanodisc based nanogenerators increases due to surface passivation and reduction of oxygen vacancies.