Homogeneous cuprous oxide (Cu 2 O) nanoparticles with size of 8–10 nm are deposited on multiwall carbon nanotubes (MWNTs) by a polyol process using Cu(CH 3 COO) 2 ·H 2 O as a precursor and diethylene glycol as both solvent and reducing agent. The composition of the resulting Cu 2 O/MWNTs composites is confirmed by XRD pattern, XPS spectrum and HRTEM images. With the change of the reaction conditions, it is found that Cu 2 O nanoparticles on the surface of MWNTs can be leafage-like or big spherical particle coated on the surface of MWNTs. HRTEM images indicate that all the leafage-like and big spherical particles are assembled by small Cu 2 O particles with size of about 2–5 nm. With the assistance of FTIR spectrum, a tentative mechanism is proposed for the formation of Cu 2 O nanoparticles with different morphologies on the surface of MWNTs.