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A micro-emulsion method was used to prepare TiO2-coated carbon nanotubes (ME-TCNTs). The physico-chemical properties of these composites were characterized by modern analytical tools. Crystalline TiO2 within the composites was composed solely of anatase. Carbon nanotubes (CNTs) within the composites were virtually uniformly covered with TiO2. CNT addition increased the surface area and the amount of hydroxyl groups on the composite surface, which suppressed the recombination of photo-generated electron/hole pairs (excitons). The composite photoactivity was greater than that of pure TiO2 and the commercial photocatalyst P25 for methylene blue degradation, predominantly due to the effect of CNT addition. An optimal TiO2 loading of 12% was found to result in the highest photoactivity in comparison with other two loadings (6% and 15%). Too little TiO2 or excessive CNT addition shielded the TiO2 and reduced the UV intensity, due to photon scattering by the bare CNTs. However, a high TiO2 content was found to be ineffective in suppressing exciton recombination because of the large distance between the TiO2 and CNTs. The photoactivity of ME-TCNTs was greater than that of TiO2 coated carbon nanotubes (TiO2-CNTs) prepared by the sol–gel method. The uniform nanometer-scale TiO2 layer on the CNT surface provided a high concentration of surface hydroxyl groups, a low exciton recombination rate and a high surface area.