We report a new result on the characterization of Nd-doped ceria, Ce_1-xNd_xO_2-x/2(x=0:075-0:675) using positron lifetime spectroscopy (LTS) and coincidence Doppler broadening (CDB) measurements. A systematic increase in lifetime that is attributedto formation of Nd-oxygen vacancy associates is seen from x=0:075–0.4 followed by a sharper increase up to x=0:5. The changein profile of lifetime around x=0:4 suggests drastic increase in the concentration of these associates. Discontinuity in lifetime around x=0:5 is ascribed to ordering of oxygen vacancies. Coincidence Doppler broadening measurements indicate reduction in the overlap of positron wavefunction with oxygen core electrons due to trapping of positrons. Low-temperature (50–300K) lifetime measurements indicate the presence of Rydberg-like positron states associated with Nd³⁺sites