Abstract: Stable dispersions of carbon nanotubes in aqueous solution and their interactions with proteins play a crucial role in the realization of biomedical applications of carbon nanotubes. In this work, multiwalled carbon nanotubes (MWCNTs) were oxidized by a concentrated H2SO4 and HNO3 mixture with the aid of ultrasonication to obtain a surfactant free stable aqueous solution with concentration of MWCNTs of 0.23mg/mL. High and ultra highspeed centrifugation were applied to the aqueous solution to yield MWCNTs in deposits and in supernatants, which were characterized by scanning electron microscopy, dynamic light scattering, UV/VIS/NIR spectrophotometry, and X-ray photoelectron spectroscopy. Results showed that oxygencontaining groups including carboxyl acid group were introduced into the MWCNTs and their length were shortened from ~50μm to 500-800nm. The MWCNTs in the supernatants subjected to different centrifugal rates had the same average length and a similar length distribution pattern. The MWCNT aqueous solutions displayed specific adsorption at 253nm, which was used to determine the amount of MWCNTs dispersed in water by a spectral analysis. The nonspecific adsorption between MWCNTs and single albumin, single fibrinogen, and the dual proteins was investigated using sodium dodecyl sulphate-polyacrylamide gel electrphoresis, and spectrofluorometry. It was demonstrated that MWCNTs preferred to adsorb fibrinogen of albumin. Modification of MWCNTs by polyethylene glycol (PEG)-750 suppressed the fibrinogen adsorption.