The photodegradation of methylene blue in aqueous solutions is studied using various photocatalysts, including neat TiO2, CNT-TiO2, Au-TiO2, and Au-CNT-TiO2 composites MB. Materials were synthesized and extensively characterized by XRD, TEM, DRFIT spectroscopy, N-2 adsorption-desorption isotherms, as well as diffuse reflectance UV-vis spectroscopy. By using CNT-TiO2 composite as catalysts, it was found that CNT act as adsorbent and photosensitizer to improve the photoactivity of neat TiO2. Among the CNT-TiO2 composites with different CNT weight ratio (0.2-20%), the 2%CNT-TiO2 shows the best photoactivity. When CNT content is larger than 2%, the surplus CNT may absorb and scatter light photons. Combined with the decrease of TiO2 amount in composite, the photoactivity is reduced. To further improve the photoactivity of 2%CNT-TiO2, different Au loads varying from 0.25% to 1% were introduced by the deposition-precipitation method. The 0.25%Au-2%CNT-TiO2 composite had the highest photoactivity. The increase in activity was explained by the surface plasmon resonance of Au that makes the composite to absorb more photons than the 2%CNT-TiO2, thus overcoming the disadvantages of surplus CNT addition. On the other hand, 0.25%Au-2%CNT-TiO2 composite also presents higher activity than 0.25%Au-TiO2 due to higher adsorption capacity provided by CNT introduction. The addition of CNT and Au simultaneously has a much stronger synergic role than when each of them is introduced individually. (C) 2012 Elsevier B.V. All rights reserved.