The geometries, electronic structures, and stabilities of MSi 14 clusters (M=Sc–Ni) have been studied by using density functional theory. The results demonstrate that the cage composed of fourteen Si atoms can completely encapsulate a 3d transition-metal atom. The binding forces of MSi 14 clusters mainly origin from the electrostatic and orbital interactions. In binding (or embedding) energy calculation, the Wigner–Witmer spin conservation rule is needed in the cases of CrSi 14 and MnSi 14 . Among MSi 14 clusters, only CrSi 14 shows the highest stability and chemical inertness simultaneously, indicating that only 20-electron rule can be applied to MSi 14 species.