Herein, a facile way to synthesize Cu nanoclusters (CuNCs) has been proposed while insulin played the role as a stabilizer. Specifically, this type of CuNCs existed in tunable diameters of 4-5 nm, and exhibited bright reddish-orange fluorescence with a quantum yield of 7.4 %. Interestingly, the fluorescence intensity of CuNCs could be obviously enhanced and more stable by introducing Eu3+. Moreover, this proposed Eu3+@CuNCs with low toxicity and near-infrared fluorescence may provide potential to broaden avenues for various applications in bioimaging and beyond.