Abstract: The geometries, stabilities and electronic properties of the ruthenium-doped silicon clusters RuSin (n = 1-14) have been systematically investigated using density functional theory method at the B3LYP/6311SDD level. Our results show that the ground state structures of RuSin change from planar to three-dimensional for n 3. The equilibrium site of the Ru atom in RuSin gradually changes from convex, surface, to interior of the cluster as the number of Si atoms varying from 1 to 14. Starting from n = 12, the Ru atom completely falls into the center of the Sin frame, forming Ru-centered Sin cage-like structures. Three-centered bonds were calculated to ensure the stability of the ground state structure. Besides, the average binding energies, second order energy differences, HOMO-LUMO gaps, vertical ionization potentials, vertical electron affinities and charge transfers were also discussed for the lowest-lying RuSin (n = 1-14) isomers. According to a relatively large Eb and ?2E values, the RuSi12 cluster with Ru-centered perfect hexagonal prism structure has higher stability.