Li-7 NMR measurements have been performed to study milling effects on ionic diffusion in lithium cobalt oxide, LiCoO2 and piezoelectric compound, LiNbO3 prepared by mechanical milling method. The milling process gives quite different effects on NMR spectra of these compounds. Both Li-7 MAS and static NMR spectra of the milled LiCoO2 show the line broadening with increasing milling time. Co-59 static spectra also show specific changes in the line shape with increasing milling time. These results would be attributed to the change in an electronic state of Co 3d orbitals because of charge compensation associated with oxygen vacancies and/or defects. Li-7 static NMR spectrum of milled LiNbO3 shows complicated line shape with increasing milling time. It is explained by superposition of two spectra arising from mobile Li+ ions and non-mobile ones settled on the fixed site. It is shown that the ratio of mobile Li+ ions increases up to a maximum of 9.4% with increasing milling time. Milling effects on the Li+ ionic diffusion in LiCoO2 and LiNbO3 are discussed in connection with changes in local structure. (C) 2008 Elsevier B.V. All rights reserved.