The possible ReSin (n = 1-12) clusters are investigated systematically at the UB3LYP level employing LanL2DZ basis sets for a sequence of different spin states. The total energies and equilibrium geometries, as well as natural populations and natural electron configurations, are calculated. The emphasis on the stabilities and fragmentation energies as well as on electronic properties is presented and discussed. Theoretical results on natural populations reveal that the natural populations of 5d and 6s orbitals of the Re atom in ReSin (n = 1-12) clusters are associated with the number of silicon atoms and spin of this species considered, that the natural population of the Re atom in the most stable ReSin (n = 1-12) clusters is recorded as negative, and that the charges in the most stable ReSin (n = 1-12) transfer from Si atoms and 6s orbitals of the Re atom to 5d orbitals of the Re atom. Therefore, the Re atom, which acts as an acceptor, plays an important role in the stability of ReSin (n = 1-12) clusters. Furthermore, the charge-transfer of ReSin (n = 1-12) depends on the spin of the species considered. Theoretical results of equilibrium geometries on ReSin (n = 1-12) clusters show that the Re atom of the most stable ReSin (n = 1-7) occupies a surface site and absorbs on the surface site of the Si cluster; however, the Re atom of the most stable ReSin (n = 8-12) clusters is trapped in the center site of the Si cluster and directly interacts with all atoms simultaneously with nonequivalent bond lengths; this observation of transition metal (TM) behavior in TM-silicon clusters being favorable to the center site of the silicon frame when n > 7 is in good agreement with experimental measurement on TbSix- (x = 6-16) clusters. Growth patterns of ReSin (n = 9-12) clusters are discussed showing the sandwichlike structure as the favorable structure. Relative stability is discussed upon removing one silicon atom, showing that ReSi2 and the sandwichlike ReSi12, ReSi11, and ReSi9 clusters have enhanced stability which is regarded as the abundance of the mass spectrometric observation on ReSin+ (n = 1-11). These theoretical results are consistent with the atomic averaged binding energies also. Comparisons of ReSi, (n = 1-12) with available theoretical results of MSin (n = 1-6, M = Cr, Mo, W, Ir) cluster series and experimental measurements are made.