The　effect　of　electron　beam　on　the　microstructures　and　phase　transformation　of　nanostructured　TiO2　heat　treated　at　various　temperatures　for　different　time　was　studied　by　in-situ　TEM　and　SAED.　Anatase　ex-situ　heated　at　250　°C　and　360　°C　transformed　to　rutile　while　irradiated　by　the　electron　beam.　With　the　increasing　sizes　and　distribution　of　the　powders　on　the　amorphous　carbon,　the　process　of　phase　transformation　by　the　electron　beam　was　encumbered.　These　evolutions　may　be　due　to　the　changes　of　vacuum　atmosphere　and　the　properties　of　powders.　©　2007　Wuhan　University　of　Technology　and　Springer-Verlag　Berlin　Heidelberg.