The crystal structure of the deficient perovskite Nd1/3NbO3 has been determined at room temperature, using electron microscopy observations and X-ray powder diffraction data. Electron diffraction study and HRTEM images evidence the doubling of a and b parameters and confirm one of the c-parameter with respect to perovskite unit cell. The structure refinement has been carried out using the orthorhombic Cmmm space group. The Nd3+ cations occupy randomly and alternatively the (00l) planes and Nb5+ cations distorted octahedral sites. This structure is characterized by the presence of empty Nd3+ sites in every second layer and the tilting of the octahedral sites around the b-axis. In addition, electron diffraction patterns exhibit weak additional diffuse reflections, which supposes some ordering of the Nd vacancies.