Unique　nanorod-like　mesocrystals　constructed　from　ultrathin　rutile　TiO　2　nanowires　were　successfully　fabricated　for　the　first　time　using　a　low-temperature　additive-free　synthetic　route,　and　the　mesocrystal　formation　requirements　and　mechanism　in　the　absence　of　polymer　additives　were　discussed.　The　ultrathin　nanowires　were　highly　crystalline　and　their　diameters　were　found　to　be　ca.　3-5　nm.　The　rutile　TiO　2　mesocrystals　were　formed　through　homoepitaxial　aggregation　of　the　ultrathin　nanowires　via　face-to-face　oriented　attachment,　accompanied　and　promoted　by　simultaneous　phase　transformation　from　the　precursor　hydrogen　titanate　to　rutile　TiO　2.　The　rutile　TiO　2　mesocrystals　thus　synthesized　were　subjected　to　detailed　structural　characterization　by　means　of　scanning　and　transmission　electron　microscopy　(SEM/TEM)　including　high-resolution　TEM　(HRTEM)　and　selected　area　electron　diffraction　(SAED),　X-ray　diffraction　(XRD)　and　Raman　spectroscopy.　The　rutile　TiO　2　mesocrystals　were　tested　for　lithium-ion　intercalation　and　demonstrated　large　reversible　charge-discharge　capacity　and　excellent　cyclic　stability,　which　could　be　attributed　to　the　intrinsic　characteristics　of　the　mesostructured　TiO　2　constructed　from　ultrathin　nanowires　offering　large　specific　surface　area　for　intercalation　reaction　and　easy　mass　and　charge　transport,　as　well　as　sufficient　void　space　accommodating　volume　change.　©　2011　The　Royal　Society　of　Chemistry.