Diamondlike carbon (DLC) deposited by focused-ion-beam chemical vapor deposition (FIB-CVD) has the interesting material characteristics because DLC deposited by FIB-CVD using the gallium (Ga) FIB contained Ga. The DLC wires were subjected to annealing, and it was found that their resistivity and the Ga content of DLC decreased. To understand the reason for the decrease in resistivity, changes in the fine structure and composition of DLC due to annealing were examined by transmission electron microscope electron energy loss spectroscopy and Rutherford backscattering spectroscopy/elastic recoil detection analysis, respectively. The results revealed that the graphite content of DLC increased due to hydrogen (H) elimination induced by annealing. Thus, it was concluded that the resistivity of the annealed DLC wires decreased due to the increase in the graphite content of DLC.