Abstarct: Abstract In this research, Cu/Ag nanoparticles and RGO/Cu/Ag nanocomposite were synthesized by green method using Citrus paradisi peel extract. Citrus paradisi peel extract played a reducing and stabilizing role in the synthesis process of nanoparticles. Nanoparticles and synthetic nanocomposite were identified by methods such as UV-Vis, FT-IR, XRD, FE-SEM, EDS and Raman. The activity of Cu/Ag nanoparticles was investigated in the process of detection of mercury (II) by colorimetric method and photocatalytic degradation under radiation. In fact, the solution color change of prepared synthetic nanoparticles in the presence of mercury (II) from yellow to pink is the baxse of this colorimetric sensor. The FE-SEM micrographs recorded after addition of mercury (II) solution shows the aggregation of synthetic nanoparticles in the presence of mercury (II). In the process of photocatalytic degradation, the efficiency of Cu/Agx nanocomposite was investigated and the influencing factors were investigated. baxsed on the results, Cu/Ag0.10 was selected as the optimal catalyst, which is used to complete the reaction in 40 minutes. In the next step, the activity of RGO/Cu/Ag nanocamopsite was investigated in reduction reaction of 4-nitrophenol using sodium borohydride. Synthetic nanocomposite has shown good catalytic activity in reducing 4-nitrophenol to 4-aminophenol.