We have studied the electronic structures of icosahedral Ti-N clusters (N = 13, 19, 43, and 55) by using a real-space first-principles cluster method with generalized gradient approximation for exchange-correlation potential. The hexagonal close-packed and fee close-packed clusters have been studied additionally for comparisons. It is found that the icosahedral structures are the most stable ones except for Ti-43, where fcc close-packed structure is favorable in energy. We present and discuss the variation of bond length, the features of the highest occupied molecular orbitals and the lowest unoccupied molecular orbital, the evolution of density of states, and the magnetic moment in detail. The results are in good agreement with the predictions from the collision-induced dissociation and size-selected anion photoelectron spectroscopy experiments. (C) 2004 American Institute of Physics.