Silver nanocrystals with tetrahedral shapes and {111} faces have been synthesized by the light-driven growth method in an aqueous solution. The nanocrystals of T-d symmetry were formed under the effect of tartrate and citrate as the structural-directing reagents at the appropriate stages of reaction. Further, the nanocrystals may be assembled through electrostatic interaction to develop large-scale particle surfaces with sharp vertexes, which can generate strong localized electromagnetic field for surface-enhanced Raman scattering (SERS) studies. Benzenethiol was used as the probe to evaluate their SERS enhancement, and enhancement factors of up to 106 are reached. As a kind of promising material, these novel nanocrystals will be applied in surface enhanced spectroscopy and plasmonics field.