AbstractWater has been proven to be an effective additive to enhance the growth rate and purity of the synthesized carbon nanotubes (CNTs) in the chemical vapor deposition (CVD) method. Due to similar CNT growth parameters in CVD and flame environment, it is expected that a similar effect can be replicated in CNT flame synthesis to a certain degree. The present study analyzes the effect of water addition to the fuel stream toward the CNT growth in methane diffusion flame under atmospheric conditions. Water vapor was introduced into the fuel gas by passing the methane gas through a water bubbler, and the growth condition was analyzed based on a cross-sectional analysis of the grown CNT on top of nickel wire. The water addition to the fuel reduces the axial extent of the growth region due to the reduction in flame height. Even though the spatial distribution of the growth region in the flame with water additive changes compared to that of the flame without water, the average growth region temper.....