This experimental study is aimed at investigating the formation and growth of carbon nanotubes by using inverse co-flowing diffusion flames. The flame appearance and flame stability under the influences of oxidizer and fuel concentrations and inner/outer velocity ratios were firstly studied. The results showed that raising the concentration of oxygen or fuel increased the flame intensity, and in turn decreased the critical fuel concentrations for the occurrence of yellow flame. However, with increasing the velocity of oxygen/nitrogen mixture, the sooty zone became narrower, leading to the increase of the critical fuel concentration where yellow flame took place. Thereafter, we employed a sampling grid (Ni) used for transmission electron microscopy as the catalytic metal substrate for the nanotube growth. Synthesis of canbon nanotubes was successfully found from laminar co-flowing oxygen-enriched ethylene diffusion flames. The horizontal sampling approach (with the grid plane normal to the burner axis) to collect deposited materials, carbon nanotubes grew much more and longer than the horizontal sampling approach (with the grid plane parallel to the burner axis) at the critical concentration where yellow flame occured. However, at the fuel concentration higher than the critical concentration where yellow flame took place, there were higher radical concentrations as the grid was placed at a higher position. Therefore, at this condition using the horizontal sampling approach to collect deposited materials was superior to the vertical sampling approach. Furthermore, for the same sampling approach, the position near the flame front had a greater carbon nanotube harvest than that far from the flame front. Straight and bamboo-like carbon nanotubes were observed in the HR-TEM images. We assumed that the particles in the carbon nanotubes are nickel oxide. It is evidenced that carbon nanotubes are produced by the heat source and carbon source in the inverse diffusion flame with the metal catalyst (Ni).