Graphene oxide (GO) was firstly prepared from graphite flake powder according to a modified Hummers method. Subsequently, we developed a one-step hydrothermal method to prepare a three-dimensional (3D) cobalt loading TiO2/RGO architecture nanocomposites by using Ti(SO4)2 and CoCl2 as precursor and Polyetheylenimine (PEI) modified graphene oxide sheets as a support. PEI is used as the connection linker to successfully achieve in situ growth of TiO2 on reduced graphene oxide surfaces among the composites. Their structure and photoelectrical properties were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis absorption spectroscopy, and X-ray diffraction. The photocatalytic activities of the nanocomposites with respect to methylene blue (MB)were also investigated under UV and visible illumination. The results showed that the nanocomposites exhibited high catalytic performancetoward methylene blue with a high degradation efficiency above 99 % in aqueous solution. Meanwhile, the catalyst was recycled over ten times without showing a signi?cant loss in its activity.