In this paper, we describe the observation of nanostructure formation under microwave processing of zirconium diboride powder with aluminum oxide. These nanostructures appear to be formed from arcing resulting from a microwave-induced electric field across conductive ZrB2 particles. Microwave heating allows process times <1 min. The arcing rapidly heated the ZrB2 and nearby alumina creating nanotubes and nanorods. The morphology of these nanostructures was characterized using scanning and transmission electron microscopy (TEM), showing ∼100 nm tube wall thicknesses with widths up to a few micrometer and lengths to 40 μm. Energy-dispersive X-ray spectroscopy showed the composition of the nanotubes included aluminum, oxygen, zirconium, and boron. Fast Fourier transform's of the TEM images provided characterization of the lattice parameters. Morphology, composition and crystallography resemble both single-crystal aluminum borate and boron-mullite nanotubes. The produced nanostructures could be used to reinforce high-temperature materials, improve the durability of metal surfaces or as needles for intracellular drug delivery.