Multiwalled carbon nanotubes (MWNTs) coated with a thick layer of CO3O4 nanocrystals were prepared through a facile and effective method for the first time, which combined the acid treatment MWNTs and in situ decomposition of Co(NO3)(2) in n-hexanol solution at 140degreesC. TEM images show that the MWNTs are nearly fully coated with a layer of CO3O4 with an average size of 8 nm. The coating layer is 15-20 nm in thickness. The electrochemical performance in Li+ insertion and extraction reactions shows that the MWNTs/CO3O4 composites have larger lithium storage capacities and a better cycle-ability.