A surfactant is used to reduce the agglomeration of iron catalysts during the synthesis of carbon nanotubes (CNTs) and their assembly by chemical vapor deposition. The agglomeration of iron catalysts during synthesis affects the CNT diameter and number of CNT walls. Also, the agglomerated catalysts within the CNT assembly indicate an inefficient reaction of catalysts during the CNT synthesis. In this study, the non-ionic surfactant, polysorbate, is added to the CNT synthesis solution in varying amounts from 0 to 3.0 wt%. The effects of the surfactant are closely related to the crystalline perfection, diameter, and number of walls of CNTs synthesized under different concentrations of the surfactant. Here, 1.0 wt% surfactant is the most favorable concentration to achieve crystalline perfection. When the surfactant is added at more than 1.0 wt%, amorphous carbons increase, although the agglomeration of iron catalysts continues to decrease. The simple addition of this surfactant can facilitate the development of the CNT assemblies that have high mechanical and electrical properties. (C) 2013 Elsevier Ltd. All rights reserved.