In this review, we discuss the recent advancement in the shape-controlled synthesis and characterization of colloidal Au-Cu alloy nanostructures. Then we review the studies on the plasmonic properties of the Au-Cu alloy nanoparticles, which are different from that of the nanoparticles composed of pure Au or Cu due to the synergism between Au and Cu. The Au-Cu nanoparticles with tunable composition and geometry have been applied in heterogeneous catalysis for CO2 reduction reaction and many other reactions and have shown good catalytic activity. They have also been demonstrated to be effective in killing tumor cells using photothermal therapy. At the end of this review, we provide our perspective on the future work of the synthesis and applications of Au-Cu alloy nanoparticles.