Nanosized, well-dispersed titania particles were synthesized via a hydrothermal method using multiwalled carbon nanotubes (MWCNTs) as structural modifiers during the nucleation process to decrease aggregation. Synthesized TiO2/MWCNT composites containing different amounts of MWCNTs were characterized using N2 physisorption, XRD, spectroscopic techniques (Raman, UV-visible, and X-ray photoelectron), and electron microscopy to illuminate the morphology, crystal structure, and surface chemistry of the composites. Photocatalytic performance was evaluated by measuring the degradation of acetaldehyde in a batch reactor under UV illumination. Average rate constants decrease in the following order: TiO2/MWCNT-1% > TiO2 > TiO2/MWCNT-5%. Addition of MWCNTs beyond the optimum loading ratio of 1:100 (MWCNT:TiO2) diminishes the effectiveness of the photocatalyst and the synergistic effect between MWCNTs and TiO2. The primary mechanism for photocatalytic activity enhancement in TiO2/MWCNT-1% is thought to be due to increased porosity, hydroxyl enrichment on the surface, and high dispersion of TiO2 particles.