We report the first direct measurement of surface hydrophilicity-hydrophobicity in multiwall carbon nanotubes (MWNTs) by analyzing the binary solvent adsorption excess isotherms of freshly oxidized as well as thermally annealed MWNT samples. Heat-induced changes in the sample morphology are monitored by XRD and N-2 adsorption isotherms, the hydrophilic-hydrophobic surface ratio is calculated from ethanol-cyclohexane adsorption excess isotherms. The surface fractal dimension and the dimension of the capillary condensation are also determined. Results obtained from these independent methods correlate well with each other. The character of the MWNT surface gradually turns from hydrophilic (no treatment) into hydrophobic (12 h in N-2 at 1673 K) upon heating. The suggested method appears to be a feasible, reliable, fast, and economic technique of characterizing MWNT surface properties.