Synthesis of carbon nanotubes with different concentrations of ferrocene (C10H10Fe) as catalyst (5.33, 10.66, 13.99-19.99 wt%) from waste engine oil precursor has been done to study its effects on the growth of carbon nanotubes. Thermal chemical vapor deposition method was used in this study. The synthesis process lasted for 30 minutes under argon gas ambient in constant precursor vaporization and synthesis temperature of 450°C and 750°C respectively. The characterization of prepared samples were done using field emission scanning electron microscopy, micro-Raman spectroscopy and thermogravimetric analysis. High density carbon nanotubes was produced at 17.99 wt% catalyst concentration with purity of 72%. The results show that the structure, diameter size and quality of carbon nanotubes are highly affected by the catalyst concentrations.