The equilibrium structures and electronic properties such as relative stabilities, electron affinities, and charge transfer of small neutral and charged FeSin(-1,0,+1) (n = 1-6) clusters have been systematically studied using the high level of the correlation consistent Composite Approach (ccCA) method. The lowest-energy geometries of these clusters can be regarded as \"substitutional structure.\" It is derived from Sin + 1(and/or Si-n + 1) clusters by replacing a silicon atom with an iron atom. The adiabatic electron affinities (AEAs) and the adiabatic ionization potentials (AIPs) have also been predicted by ccCA schemes for FeSin(n = 1-6) and their ions. The dissociation energies of an iron or a silicon atom from the ground-state structure of FeSin clusters have been evaluated to check relative stabilities of FeSin(-1,0,+1) (n = 1-6) clusters. Compared with other clusters, neutral and charged FeSi2 possess higher stability. As for the neutral clusters and the negatively charged ions, the theoretical charges of the iron atom in FeSin (n = 1-6) species (except for FeSi and FeSi2-) show that silicon clusters act as an electron donor. For the cationic species, however, the charge transfers from iron atom to silicon clusters (except for FeSi3+) show that the iron atom acts as electron donor.