A study has been made of the electric conductivity and structure of Ar ion implanted diamonds depending on the target temperature during Ar implantation. Implantations using 150 keV Ar ions with a dose of 2 × 1016ions/cm2were carried out. The target temperature was maintained either at -60°C or at 200°C. Two types of implanted diamonds were prepared. Each consisting of two implantations was implanted at -60°C, and then at 200°C, whereas the other was implanted at 200°C, and then at -60°C. Each sample was implanted four times in such a way as to use the reversed target temperature. After each implantation, the sheet resistivity was measured by a four point probe method at room temperature, and the structure was investigated by laser Raman spectroscopy. The sheet resistivity varied by two or more orders of magnitude, depending on the target temperature. Raman spectra showed that the surface structure for the specimen implanted at -60°C is amorphous-like, and ion implantation at 200°C reduces disordered-graphite containing amorphous zones. Ar implantation at -60°C in the 200°C-implanted diamond or that at 200°C in -60°C-implanted diamonds results in change in the sheet resistivity and structure which is dependent on the target temperature of additional ion implantation. It is concluded that the target temperature at the final stage of implantation plays an important role in forming different structure in implanted diamonds and results in change the sheet resistivity.