Engineered nanomaterials such as ZnO nanoparticles (NPs) will inevitably enter the environment because of the large quantities produced and their widespread application. Plants comprise a fundamental living component of terrestrial ecosystems; thus, understanding the interaction between ENMs and plants is important. In the present study we conducted an integrated study by employing a combination of microscopic and spectroscopic techniques to comparatively investigate the uptake of ZnO NPs and Zn2+ ions by maize in order to further elucidate plant uptake pathways of ZnO NPs. The results demonstrate that the majority of Zn taken up was derived from Zn2+ released from ZnO NPs, and Zn accumulated in the form of Zn phosphate. ZnO NPs were observed mainly in the epidermis, a small fraction of ZnO NPs were present in the cortex and root tip cells, and some further entered the vascular system through the sites of the primary root-lateral root junction. However, no ZnO nanoparticle was observed to translocate to shoots, possibly due to the dissolution and transformation of ZnO NPs inside the plants.