Density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were employed to investigate the electronic and nonlinear optical properties of some substituted C2Bn −2Hn (n = 14 −17) carboranes. Li, Na, K, F, Cl, Br are used as substituents. The carboranes substituted with alkali metal show considerably large first hyperpolarizability values than those of un-substituted ones. NLO response of the halogen-substituted systems is slightly enhanced. The well-known two-level model theory is investigated through TD-DFT approach to understand the origin of NLO response. This study indicates that alkali-metal substituted carboranes may be appropriate for nonlinear optical (NLO) applications.