To investigate the crack resistance performance of Mg-Zn clusters in the Al-Zn-Mg-Cu alloys, the geometries and electronic properties of MgnZn and Mgn-1Zn2 (n = 1-5) clusters are calculated by the density functional theory at the P3BW91/LANL2DZ level in Gaussian09 package. Structures of MgnZn and Mgn-1Zn2 (n = 1-5) clusters are achieved by gradually substituting one Mg atom with one Zn atom in the lowest-energy Mgn+1 (n = 1-5) clusters. The results reveal that the Zn atoms tend to replace the Mg atoms which are far from the cluster center. The doped Zn atoms decrease the stability of Mg clusters. Mg3Zn and Mg3Zn2 are more stable than their neighbors by the second derivative of the binding energies. Mg3Zn and Mg2Zn2 clusters have weaker chemical activity. NBO analysis reveals that Zn atoms have spd orbital hybridization in the Mg-Zn clusters. (C) 2017 Elsevier B.V. All rights reserved.