The　metal-semiconductor-metal　junction　(M-S-M)　was　fabricated　with　an　individual　ZnO　nanowire　connected　with　a　tungsten　electrode.　Its　current-voltage　(I-V)　characteristics　were　in-situ　measured　with　a　combination　of　scanning　electron　microscopy　(SEM)　and　a　lab-built　micro-manipulator　capable　of　manipulating　things　on　nanometer　scale.　The　weak　rectification　was　observed　in　the　I-V　curve.　Interesting　finding　is　that　the　irradiation　of　an　electron　beam　of　the　M-S-M　junction　significantly　affects　its　I-V　characteristics.　For　example,　with　an　electron　irradiation　energy　of　30　keV,　the　total　resistance　of　the　ZnO　nano-wire　decreases,　and　its　calculated　conductance　and　its　carrier　density　are　found　to　be　σ=0.24　S/cm　and　n=1.64　×　1016cm-3,　respectively.　In　contrast,　the　I-V　characteristics　of　a　single　carbon　fiber　closely　contacted　with　a　tungsten　electrode　before　and　after　the　electron　irradiation　of　30　keV　show　that　the　total　resistance　remain　unchanged　with　a　conductance　of　σ=22　S/cm.