Multiwalled carbon nanotubes (MWNTs) have been Successfully decorated with magnetic CoO and NiO nanoparticles via the interaction of M(NH3)(x)(2+) (M = Co,Ni) ions and the carboxyl groups on the surface of acid-treated MWNTs. The obtained composites were characterized by X-ray diffraction, scanning electron and transmission electron microscopies. The soaking time plays an important role in the preparation of the composites. Magnetic measurements indicate that both the CoO/MWNT and NiO/MWNT composites present superparamagnetic behavior which can be attributed to the small size of CoO and NiO nanoparticles. (C) 2009 Published by Elsevier Inc.