We present in this paper the memory characteristics of doubly stacked nonvolatile nano-floating gate memory (NFGM) devices with channels of single ZnO nanowires. In our doubly stacked NFGM devices, first- and second-stage floating gate layers composed of Al nanoparticles (NPs) are separated with a 3-nm-thick interlayer of Al2O3. The average size of Al NPs created by sputtering is about 7 nm, and the Al NPs are isolated from each other laterally in the same layer as well as vertically in the double layers. When the voltage is swept from 10 to -10 V, the flat-band voltage shifts are about 0.8 and 2.5 V for the singly and doubly stacked MOS capacitors, respectively. The comparison of metal-oxide-semiconductor capacitors embedded with singly and doubly stacked nanoparticle layers reveals that the retention characteristics of the doubly stacked NFGM device are superior to those of a singly stacked NFGM device. Furthermore, the memory characteristics of the doubly stacked NFGM device remain even after 10(5) programming and erasing cycles.