Ethane was successfully used as an active and efficient carbon source in a large scale synthesis of high quality carbon nanotubes by chemical vapour deposition (CVD) over Fe/Al2O3 catalyst with an iron loading of 20 wt.%. The carbon nanotubes yield of 20 g per gram of catalyst per hour was obtained at a synthesis temperature of 660 °C. The active phase for growing carbon nanotubes is a mixture of a metastable iron carbide (Fe3C) and α-Fe which were formed in situ by the ethane dissociation followed by carbon diffusion through the starting α-Fe phase similarly to that reported in the literature. The reaction products only contained multi-walled carbon nanotubes with very homogeneous diameters between 20 and 40 nm and lengths up to several hundred nanometers without any trace of other impurities such as nanoparticles or amorphous soot. The high yield of the MWNT significantly decreases the amount of the catalyst in the final product and the product can be used directly without need for post-synthesis treatment in order to remove the catalyst. Ethane is an active carbon source for growing MWNTs with high yield and selectivity. The reaction temperature should be keep ≤750 °C as synthesis carried out at 800 °C under similar reaction conditions led to the formation of amorphous soot and carbon nanoparticles mixed with nanotubes.