Nanocrystalline (n) LiNbO3 was prepared by high-energy ball milling from the polycrystalline (p) material. Grain sizes were determined by XRD measurements and TEM images; thermal stability ranges of the samples were examined by DTA. NMR investigations of the diffusion-induced Li-7 spin-lattice relaxation (SLR) rate T-1(-1) of n-LiNbO3 in the temperature range from T = 140 to 460 K at frequencies between upsilon = 24 and 78 MHz revealed a reduced activation energy on the low-temperature side of the typical peak in a log T-1(-1) vs T-1 plot in comparison with results obtained from experiments performed on the p-material between 300 and 1400 K. Corresponding measurements of the SLR rate in the rotating reference frame yielded an asymmetric peak in the case of p-LiNbO3, in contradiction to standard BPP theory, whereas in n-LiNbO3 only a weakly temperature-dependent relaxation rate background was observed. Furthermore, neither in n-nor in p-LiNbO3 BPP-type frequency dependencies of the SLR rate, i.e., T-1(-1) proportional to upsilon(-beta) with beta = 2, were found. The determined values ranging from beta = 1.1 to 1.5 are ascribed to the influence of structural disorder and Coulomb interaction on the diffusive motion.