LaBO3 bundle-like nanorods are self-assembled through a novel oxide-hydrothermal method. In this route, the stoichiometric amounts of La2O3 and boric oxide B2O3 are mixed in proper amounts of water in a surfactant/ligand-free sealed hydrothermal system. The nanobundles are de-agglomerated to nanorods by tiny Sm3+ replacing La3+. The characterization of these materials has been carried out by X-ray powder diffraction, FTIR, thermo-gravimetric and differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction. As-prepared aragonite-type LaBO3 nanorods are fairly controlled to have a high purity, homogeneous, and bundled morphology composed of numerous nanorods with diameter ca. 90 nm. The formation processes and mechanics of LaBO3 nanobundles and nanorods are investigated. The room-temperature fluorescence properties of various Sm3+-doped LaBO3 are investigated.