Abstarct: In this this thesis in order aimed to investigate the effect of graphene(2.5mg, 5mg, 10mg) on the structural, optical and photocatalysis properties of copper oxide, CuO-graphene nanocomposites were synthesized with copper acetate, graphene, Sodium hydroxide and CTAB precursors by hydrothermal method. Then their Structural, optical and photocatalytic properties were investigated. The result of the structural study indicated the formation of monoclinic copper oxide and hexagonal graphene crystal structures. Comparing the structural properties of the samples exhibited that the synthesized nanocomposite with 5mg of graphene has a better structural quality. The optical properties of the samples showed that the band gap of nanocomposites was reduced compared to the pure copper oxide sample. In this work, photocatalytic properties of the samples to determine the effect on pollutant degradation of methylene blue dye. The results indicated that with increasing graphene in CuO-graphene nanocomposite up to 5mg efficiency of photocatalytic activity significantly (about 56%) increases and then significantly decreases. The obtained results indicated the nanocomposite with 5mg graphene has better photocatalystic activity.