Applications　of　atomic　force　microscopy　(AFM)　to　the　fabrication　of　chemical　nanosensors　are　presented　in　this　paper.　Using　AFM　cantilever　as　cathode,　the　surface　of　Ti　thin　film　is　oxidized　to　form　a　few　tens　of　nanometers　wide　oxidized　metal　semiconductors　wire,　which　works　as　a　nanowire-based　hydrogen　sensor.　The　reaction　mechanism　is　proposed.　The　AFM　observations　of　fabrication　of　a　TiO2　nanowire　are　carried　out.　The　sensitive　characteristic　of　such　TiO2　nanowires　to　hydrogen　is　investigated.　(C)　2008　Elsevier　B.V.　All　rights　reserved.