To accelerate the development and design of magnesium (Mg) alloys, the structural and mechanical properties of important precipitates in Mg-Zn alloys were studied by experiments and density functional theory. The nano-indentation tests revealed that the hardness of the precipitates initially increased and then decreased with increasing Zn content, and was significantly higher than that of pure Mg and Zn. The calculation results revealed that the precipitates stability initially increased and then decreased with increasing Zn concentration. The bulk moduli of the precipitates increased, whereas their shear and Young’s moduli initially increased and then decreased with increasing Zn content. The decreasing order of ductility for these compounds is MgZn₂ > Mg₂₁Zn₂₅ > Mg₂Zn₁₁ > Mg₄Zn₇. The surface profiles of the compounds revealed that they are obvious anisotropy. Both the degree of covalency and bond length of covalent bonds initially increased and then decreased with increasing Zn content.