Silicon nanocrystals in a range from 2 nm to 5 nm were prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits that the reaction be completed in only a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanocrystals measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph confirmed the material identity of nanocrystals as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that are chlorine-or butyl-capped. The emission peak center moved to a longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation.