We　investigated　the　correlation　of　thermodynamics　and　grain　growth　kinetics　of　nanocrystalline　metals　both　theoretically　and　experimentally.　A　model　was　developed　to　describe　the　thermodynamic　properties　of　nanograin　boundaries,　which　could　give　reliable　predictions　in　the　destabilization　characteristics　of　nanograin　structures　and　the　slowing　down　of　grain　growth　kinetics　at　a　constant　temperature.　Both　the　tempera　tu　re-varying　and　isothermal　nanograin　growth　behaviors　in　pure　nanocrystalline　Co　were　studied　to　verify　the　thermodynamic　predictions.　The　experimental　results　showing　that　discontinuous　nanograin　growth　takes　place　at　a　certain　temperature　and　grain　growth　rate　decreases　monotonically　with　time　confirm　our　thermodynamics-based　description　of　nanograin　growth　characteristics.　Therefore,　we　propose　a　thermodynamic　viewpoint　to　explain　the　deviation　of　grain　growth　kinetics　in　nanocrystalline　metals　from　those　of　polycrystalline　materials.　(c)　2006　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.