Abstract The geometrical structure, electronic structure and chemical bond properties of the gas-phase GaMg n - (n=2-12) clusters were studied utilizing CALYPSO software as well as density functional theory (DFT). It is shown that tetrahedral-like and pyramidal-like structures are the two "seeds" for GaMg n - (n=2-12) clusters growth. Relative stability calculations indicate that GaMg 8 - cluster possesses the most robust stability and is a reasonable candidate for the "magic" cluster. NCP calculations confirm that Ga and Mg atoms play the roles of receiving and losing electrons, respectively.NEC analysis further yields that valence orbital electron transfer is s→p. ELF analysis shows that Mg-Mg covalent bonds start to appear in GaMg 2 - size, which is much earlier than in other "heavy" metal-doped magnesium. For the most stable GaMg 8 - cluster, UV-Vis, IR and Raman spectroscopic predictions were also performed specifically, and the excited state properties of this cluster were investigated by the hole-electron method and NTO.