ZnO–TiO2–carbon nanotubes (CNTs) composites are successfully synthesized using microwave-assisted reaction of ZnO precursor in TiO2 and CNTs suspension using a microwave synthesis system and they are used as photocatalysts for photocatalytic reduction of Cr(VI). The results show that the CNTs addition could enhance the photocatalytic performance of ZnO–TiO2 composites. The ZnO–TiO2 composites achieve a maximum reduction rate of 90% at 240 min under UV light irradiation, much higher than those for the pure ZnO (58%) and the ZnO–TiO2 (69%). The improvement is ascribed to the increased light absorption intensity and range as well as the reduction of electron–hole pair recombination with the introduction of CNTs.