We present a comparative study of single-walled carbon nanotubes grown using iron and cobalt nanoparticles as catalysts via the chemical vapor deposition approach.Monodispersed iron and cobalt oxide nanoparticleswith an average size of 2 nmwere prepared using a polystyrene-b-poly (4-vinylpyridine) diblock copolymermicelle template. The 2 nm iron oxide nanoparticles generated single-walled carbon nanotubes with an average diameter of 1.5 nmwhile 2 nmcobalt oxide nanoparticles produced single-walled carbon nanotubes with an average diameter of 1.0 nm. To achieve high growth yield using iron nanoparticles as catalyst, higher carbon feed rate is required. These findings demonstrate the importance of the synergic interaction between catalyst and carbon precursor in single-walled carbon nanotube formation. It also elucidates the important role of catalyst chemical composition on carbon nanotube properties. Copyright © 2010 John Wiley & Sons, Ltd.