The Effects of Processing Conditions upon the Yield of Carbon Nanotubes:Abstract – This research investigates the optimal process conditions to make multi-wall nano-tubes (MWNTs) and to achieve high yielding. This study applies Arc Discharge Method (ADM) to synthesize multi-wall nanotubes (MWNTs) and hollow carbon nanocapsules (HCNCs). The morphology and micro-structure of carbon nanotubes (CNTs) were observed by Transmission Electron Microscope (TEM) and Field Emission Scanning Electron Microscope (FE-SEM). The experimental result shows that the optimal process conditions for high yield of CNTs are 3.0 l/min of inert gas(Ar)flow rate, 70A of the discharged current, and 20V of the discharged voltage. In addition, the lower the cooling temperature is, the higher the yield of CNTs. The diameter of carbon nanotubes range from 10 to 20 nm and the aspect ratio of CNTs are between 100 and 600. Finally, the smaller the diameter of carbon rod is, the lower the discharged current and the yield of CNTs. Keywords: multi-wall carbon nanotubes(MWNTs)、hollow carbon nanocapsules(HCNCs)、Arc discharged method(ADM)、aspect ratio