A direct current plasma enhanced chemical vapor deposition (DC PECVD) apparatus was designed and constructed to synthesize high purity vertically well-aligned carbon nanotubes (VACNTs) at relatively low temperatures. The effect of C 2 H 2 concentration and plasma current on CNT growth was investigated. The DC PECVD synthesis of CNTs consisted of two steps: (1) reduction with gaseous H 2 and NH 3 to form catalyst nanoparticles, and (2) subsequent CNT growth in the presence of gaseous H 2 and C 2 H 2 . High-resolution transmission electron microscopy images confirmed the presence of multi-walled carbon nanotubes (MWCNTs). Their graphitic structure was then confirmed by Raman spectroscopy. Scanning electron microscopy (SEM) results illustrated the relationship between the plasma, C 2 H 2 concentration and CNT growth. Deviation of acetylene flow rate from an optimal rate led to deterioration of CNT growth. Comparing SEM images of CNTs grown with and without plasma showed that plasma had an important role in VACNT formation.