A new method termed "in situ two-phase ligand exchange" was developed to obtain alloy nano clusters. With this approach, a series of alloy nanoclusters were obtained for the first time, including Au20Ag1(SR)(15), Au21-xAgx(SR)(15) (x = 4-8), Au21-xCux(SR)(15) (x = 0, 1), and Au21-xCux(SR)(15) (x = 2-5) (R = tert-butyl). Interestingly, single-crystal X-ray crystallography (SC-XRD) shows that their frameworks are all alike except for Au21-xCux(SR)(15) (x = 2-5), indicating that more Cu dopants alter the structure. Au21-xCux(SR)(15) (x = 2-5) exhibits a significantly different configuration. The optical absorption spectra of these bimetal nanoclusters (NCs) show distinct characteristic peaks, indicating that the metal-doping remarkably affects the electronic structure of NCs. The DFT calculations were also employed for determination of NC 1-3 frameworks and understanding their optical properties.