The electron field emission (EFE) properties of Si-nanowires (SiNW) were improved by coating a UNCD films on the SiNWs. The SiNWs were synthesized by an electroless metal deposition (EMD) process, whereas the UNCD films were deposited directly on bare SiNW templates using Ar-plasma based microwave plasma enhanced chemical vapor deposition (MPE-CVD) process. The electron field emission properties of thus made nano-emitters increase with MPE-CVD time interval for coating the UNCD films, attaining small turn-on field (E-0=6.4 V/mu m) and large emission current density (J(e)=6.0 mA/cm(2) at 12.6 V/mu m). This is presumably owing to the higher UNCD granulation density and better UNCD-to-Si electrical contact on SiNWs. The electron field emission behavior of these UNCD nanowires emitters is significantly better than the bare SiNW ((E-0)(SiNWs)=8.6 V/mu m and (J(e))(SiNWs)<0.01 mA/cm(2) at the same applied field) and is comparable to those for carbon nanotubes.