Si nanometer structures are promising for exhibiting the quantum size effect at temperatures even as high as a room temperature. The present work investigates by TEM the damages induced by a heavy ion-implantation to the fine Si columns, aim of fabrication of 1-D tunneling PN diode in future. Si columns are fabricated by electron beam lithography and reactive ion etching, followed by thinning by thermal oxidation of Si . Ultra fine Si column with a diameter of 8 nm are successfully formed. TEM lattice image observations for fine Si columns, which are subject to ion-implantation and subsequent annealing, are carried out. In the case of heavy doping of As, as well as BF2, as-doped structure is amorphous, and recrystallization is observed after annealing at 1000 °C for 30 min. Typical damages such as dislocations which are parallel to the {111} planes and Si micro-crystals which are differently oriented from the Si single crystal substrate are observed for Si columns with diameters larger than 40nm. However, it should be noted that no damage is observed for fine Si columns with diameters less than 20nm. It is suggested that defects are diffused out to the surface or the Si/SiO2 interface for ultra fine Si columns during annealing.