H2Ti4O9　nanocrystals　with　high　specific　surface　areas　were　prepared　by　delamination　and　reassembly　process　through　a　way　of　ball　milling　combined　with　ion　exchange　reaction.　The　samples　were　characterized　by　X-ray　powder　diffraction,　transmission　electron　microscopy,　chemical　analysis,　thermal　analysis,　N-2　adsorption-desorption　isotherm,　and　absorption　spectrum.　The　crystallites　of　Ti4O92-　in　the　form　of　titania　nanosheets　has　lateral　size　less　than　50　nm.　The　specific　surface　area　of　H2Ti4O9　nanocrystals　depends　on　pH　value　of　reassembling　solution　and　ball　milling　time.　H2Ti4O9　nanocrystals　prepared　by　ball-milling　of　K2Ti4O9　for　2　h　and　suspending　in　1　M　HCl　followed　by　precipitation　at　pH　8　had　the　specific　surface　area　of　328.4　m(2)　g(-1)　which　was　about　16　times　larger　than　the　fibrous　H2Ti4O9　prepared　by　treating　original　K2Ti4O9　without　ball-milling　in　1　M　HCl.　(c)　2005　Elsevier　B.V.　All　rights　reserved.