The properties of multi-walled carbon nanotubes (MWCNTs) significantly affect cement paste properties. This study statistically analyzed the effects of MWCNT properties such as specific surface area, length, functional group content and outer diameter on cement paste properties, together with associated reasons. While MWCNTs with fewer functional groups, smaller surface area, shorter length and larger outer-diameter are successful in filling gel nano-micro pores, others were successful in filling micro-meso cracks. The acidic environment formed by carboxyl groups causes more void formation, while hydroxyl groups with water-absorbing structure have been effective in filling voids. Remarkable improvement ratios have been obtained in electrical resistivity (61.0%), splitting tensile strength (77.2%), CH content (51.0%), water absorption (15.2%), and porosity (6.2%) by using hydroxyl-functionalized multi-walled carbon nanotubes with a 30 nm outer wall-diameter, to replace 0.1% by weight of cement.