The lanthanum carbide alloy was induction melted in vacuum induction melting furnace from lanthanum and graphite with the mass ratio of 89:11. Lanthanum hydroxide (La(OH)3) nanopowders were prepared by a simple hydrolysis of lanthanum carbide at room temperature under normal atmospheric pressure without any surfactant. X-ray diffraction (XRD) showed that the nanoparticles were with a hexagonal structure. The effect factors such as reaction time, reaction temperature and the mass ratio of lanthanum carbide powders to H2O on BET surface area of the obtained nanopowders were investigated. Furthermore, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) showed that nanopowders behaved the morphology of short nanorod. The longitudinal growth direction of the nanorod had an angle of about 14° with the (101) lattice plane and the lateral growth direction had an angle of about 35° with the (200) lattice plane. The mechanism of formation of nanorod was discussed on the basis of the experimental results.