Using a gas mixture of propyne (C3H4) and ammonia (NH3) as a carbon precursor, we have successfully synthesized multiwalled carbon nanotubes (CNTs) by the direct current (dc) plasma enhanced chemical vapor deposition (PECVD) onto Co-sputtered glass at 550°C. As the flow ratio of NH3 to C3H4 in the mixture gas increased, the crystallinity and alignment of CNTs were improved. In addition, the field emission characteristics of CNTs were also improved. the turn-on voltage became lower, and the current density and the field enhancement factor were more increasing. Raman spectroscopy and scanning electron microscopy were utilized to confirm the effect of the gas flow ratio on CNTs. Therefore, the gas flow ratio was found to be one of important factors to govern the crystalline and field emission characteristics of CNTs. The growth mechanism of CNTs using a C3H4 gas is under investigation with the possibility that three carbon atoms in a C3H4 molecule is converted directly to a hexagon of a CNT by combining two molecules.