A facile method for preparing waster-soluble poly(vinyl alcohol)-grafted multi-walled carbon nanotubes (PVA-grafted MWNTs) was developed. Well-defined poly(vinyl acetate) chains end-capped by a cobalt(II) acetylacetonate ($Co(acac)_2$) complex [PVAc-$Co(acac)_2$] were synthesized by the cobalt-mediated radical polymerization (CMRP) of vinyl acetate. PVAc macroradicals generated by the homolytic cleavage of the carbon-cobalt (C-Co) bonds of PVAc-$Co(acac)_2$chains were then grafted directly to the MWNTs via radical addition reactions in dimethyl sulfoxide (DMSO) at $50^{circ}C$. The amount of the PVAc grafted onto the surface of the MWNTs decreased with increasing molecular weight of PVAc-$Co(acac)_2$. Hydrolysis of the grafted PVAc finally yielded PVA-grafted MWNTs, which showed good solubility in water. Surface functionalization of the MWNTs was confirmed by $^1H$ NMR spectroscopy, FTIR spectroscopy and TEM.