Lead-free　nano　(Li0.06Na0.47K0.47)NbO3　powders,　with　pure　perovskite　structure　and　various　grain　sizes　between　about　30　and　60　nm,　have　been　successfully　synthesized　by　a　novel　sol-gel　method,　in　which　Nb2O5　was　used　as　the　Nb　source.　The　refining　XRD　and　Raman　spectra　were　used　in　combination　with　TEM　to　investigate　the　evolution　of　lattice　structure　and　phase　transformation　behavior　as　a　function　of　grain　size.　The　results　demonstrated　that　the　growth　process　of　grains　has　been　divided　into　two　stages,　and　the　distortion　of　unit　cell　apparently　decreases　with　decreasing　grain　size.　At　around　35　nm,　the　phase　structure　of　(Li0.06Na0.47K0.47)NbO3　changed　from　orthorhombic　to　tetragonal.　This　phenomenon　is　related　to　a　grain　size-induced　structural　phase　transition.　For　the　well　accepted　wisdom　that　niobates　get　super　piezoelectric　properties　in　orthorhombic-tetragonal　transition　region,　our　results　suggested　a　critical　size　for　the　application　of　(Li0.06Na0.47K0.47)NbO3　in　nano　piezoelectric　devices.　(C)　2009　Elsevier　Ltd.　All　fights　reserved.