The possible geometrical and electronic structures of small TinMg (n=1—10) clusters have been optimized by using B3LYP method of density functional theory (DFT). The binding energies, energy level distribution, energy gaps, electron affinities, dissociation energy and second difference in energy are calculated and discussed. The resulting geometries show that the magnesium atom remains on the surface of clusters. The geometric effect and electronic effect clearly indicate the Ti5Mg cluster to be endowed with special stability.