In this study, the electronic and nonlinear optical (NLO) properties of a novel class of superalkalis (Li2F, Li3O and Li4N) doped silicon carbide (Si12C12) nanocages are investigated by using density functional theory (DFT) calculations. Computational results reveal that these complexes are quite stable and superalkalis prefer Sitop position of the nanocage energetically to be chemisorbed. The doping of superalkalis effectively reduced the HOMO–LUMO energy gap and transformed Si12C12 nanocage from insulator to n-type semiconductor. More interestingly, these complexes exhibited significantly large first hyperpolarizabilities (βo) in the range of 2141–19864 au. This remarkable increase in first hyperpolarizability (βo) values is due to small transition energies ΔE, which comes from the corresponding charge transfer from superalkali to the nanocage. The NLO response of the superalkali-doped Si12C12 nanocage was much better to those of their alkali-metal-doped analogs. Moreover, frequency dependent hyperpolarizability calculations are performed in the range of 400-1600 nm including 532 and 1064 nm for commonly used lasers. The TD-DFT analysis reveals that these complexes possess enough transparency in the UV region which is required besides large NLO response for practical applications in the field of opto-electronics. This study should provide new insights into the design of novel NLO materials useful for applications in all-optical switching, wavelength conversion and harmonic generation.