We report on the first use of MWCNT/nanotubular-TiO2 (multiwalled carbon nanotube, MWCNT; TiO2-derived nanotube, nanotubular-TiO2) composites as catalysts for photodegradation of aquatic humic substances (HSs). The MWCNT was demonstrated to be capable of enhancing the activity of the photocatalyst. The best degradation efficiency was obtained by using MWCNT/nanotubular-TiO2 composites having 20% MWCNTs as the photocatalyst.