Abstract: Diamond growth on W-wire and C-fiber substrates was studied. A treatment was used to separate fibers one by one from a bunch of more than 10000 fibers. The selected growth condition was to keep the carbon fiber core solid after CVD growth. Activation energy of CVD coated fibers is 93.15 kJ/mol in average. SEM pictures show surface and core morphology of the coatings under different treatment conditions. There are two different contrasts related to interior graphite carbon and exterior diamond layer. Wire fracture strength and Young's modulus measurement indicates that the fracture strength of W wire with diamond coating is 0.567 GPa, very close to its value without coating. However, the fracture strain of the wire with diamond coating is 4.8%, which is much less than that of W wire fracture strain of 7%. It means that diamond coated wire may reduce wire fracture strain and improve its mechanical property.