Water-soluble multi-walled carbon nanotubes (MWNTs) were prepared via surface-initiated atom transfer radical polymerization (ATRP) of 2-(methacrylolyoxy) ethyl phosphorylcholine (MPC) from carbon nanotubes (CNTs). The success of the surface functionalization of (CNTs). The success of the surface functionalization of MWNTs with poly(2-methacryloyloxy) ethyl phosphorylcholine) (pMPC) was ascertained using fourier transform infrared spectrophotometry (FTIR), thermogravimetric analysis (TGA), hydrogen nuclear magnetic resonance (H-1-NMR), and transmission electron microscopy (TEM). Different from the results of the previous work, in our work, we demonstrate that the amount of pMPC on CNTs can be easily regulated by ATRP approach. In addition, from TGA results, a linear relationship between the weight loss fraction of MWNT-pMPC and the weight of MPC fed and as high as 48.1% weight loss of MWNT-pMPC (MWNTs grafted by pMPC) are observed. Through TEM, the core-shell structure of MWNT-pMPC is clearly observed, which is also different from the previous report. The pMPC-modified MWNT are highly soluble, which can also resist pH and saline concentration changes and remain stable in physiological environment. PMPC-modified MWNT does not significantly affect the blood coagulation as demonstrated in plasma recalcification time (PRT) test. These highly soluble MWNTs are expected to enable their wide use in biomedical areas. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 351-357, 2009.