Retaining the morphology of gallium oxide nanostructures during structural transformations or after doping with lanthanide ions is not facile. Here we report on the sonochemical synthesis of nearly monodisperse ∼550 nm long nano-spindles of undoped and La-doped α-GaOOH. The transformation of as-prepared undoped and La-doped α-GaOOH powders into the corresponding undoped and La-doped Ga₂O₃ phases (α and β) was achieved by carrying out controlled annealing at elevated temperatures under optimized conditions. The formation of gallium oxide nano-spindles is explained by invoking the phenomenon of oriented attachment, as amply supported by electron microscopy. Interestingly, the morphology of the gallium oxide nano-spindles remained conserved even after doping them with more than 1.4 at% of La³⁺ ions. Such robust structural stability could be attributed to the oriented attachment-type growth observed in the nano-spindles. The as-prepared samples and the corresponding annealed ones were thoroughly characterized by powder X-ray diffraction (PXRD), electron microscopy (SEM, TEM, and STEM-EDS) and X-ray photoelectron spectroscopy (XPS). Finally, photoluminescence from the single-crystalline undoped and La-doped β-Ga₂O₃ was explored.