The crystalline carbon nanotubes having mesopores that are open at one end, with pore width of 4 +/- 0.8 nm, were characterized by XRD, XPS, and HRTEM. The N-2 adsorption isotherm of multiwall carbon nanotubes was measured at 77 K. A hump was observed near P/P-o = 0.4 in the adsorption isotherm, The adsorption isotherm was deconvoluted into those on the inner and external surfaces using the separately determined total, inner, and external surface areas. The adsorption isotherm on the inner surface was without adsorption hysteresis and had a sharp uptake at the P/P-o region corresponding to the mesopore width, which was ascribed to capillary condensation in the mesopores of carbon nanotubes.