The two-photon absorption (TPA) properties of the Si-n (n = 3-10) clusters were investigated by using the density functional response approach. The TPA coefficients of the Si clusters are systematically smaller than those of Si bulk for 800-2200 nm. The TPA coefficients of the Si clusters as well as Si bulk increase with a decrease of the input light wavelength. The analysis of the TPA enhancement shows that the channel of double resonance makes a significant contribution to the large TPA coefficients of the Si clusters in the visible range. (C) 2012 Elsevier B.V. All rights reserved.