This paper preliminarily investigates the general transport properties (i.e., water sorptivity, water permeability, and gas permeability) of carbon-nanotube/cement composites. Carboxyl multi-walled carbon nanotubes (MWNTs) are dispersed into cement mortar to fabricate the carbon nanotubes (CNTs) reinforced cement-based composites by applying ultrasonic energy in combination with the use of surfactants (sodium dodecylbenzene sulfonate and sodium dodecyl sulfate). Experimental results indicate that even at a very small dosage the addition of MWNTs can help decrease water sorptivity coefficient, water permeability coefficient, and gas permeability coefficient of cement mortar, which suggests that CNTs can effectively improve the durability properties of cement-based composites.