Carbon nanotubes (CNTs) were synthesized by direct spinning from chemical vapor deposition (CVD) reactions and their assembly for continuous fibers was fabricated through post-processing devices. The complicated processing parameters that include a precursor solution composition, reaction temperature, flow rate of a carrier gas, and injection rate of the precursor solution were precisely controlled to synthesize CNTs during the reaction process. The effects of the processing factors were analyzed with respect to the formation of CNTs and the crystallinity in the CNT structure. The CNT fibers were characterized by a scanning electron microscope, high-resolution transmission electron microscopy, and Raman spectroscopy. The type and crystalline quality of the CNT fibers were characterized by a Raman radial breathing mode and its relative intensities of the G and D bands. A high reaction temperature, high H-2 flow rate, and low injection rate of solution precursor were important factors to improve the crystalline quality of the CNT fibers. Low concentrations of iron catalysts in the reaction were favorable for the synthesis of single-walled carbon nanotubes (SWCNTs) that have high electric conductivity, superior specific strength, and high crystallinity. The CNT fibers could be tunable to meet a particular application by varying the reaction conditions. (C) 2013 Elsevier B.V. All rights reserved.