The displacement of oxygen lattices in Ge ion-implanted ZnO bulk single crystals is studied by nuclear reaction analysis (NAR), photoluminescence (PL), and Van der Pauw methods. The Ge ion-implantation (net concentration: 2.6×10 20 cm −3 ) into ZnO is performed using a multiple-step energy. The high resistivity of ∼10 3 Ωcm in un-implanted samples remarkably decreased to ∼10 −2 Ωcm after implanting Ge-ion and annealing subsequently. NRA measurements of as-implanted and annealed samples suggest the existence of the lattice displacement of O atoms acting as acceptor defects. As O related defects still remain after annealing, these defects are not attributed to the origin of the low resistivity in 800 and 1000°C annealed ZnO.