Silver nanocubes and nanorods were prepared with the assistance of sodium bromide (NaBr) through a developed polyol route. The addition of different amounts of NaBr could tune morphologies of silver nanostructures. Transmission electron microscopy, high-resolution transmission electron microscopy, selected areas electron diffraction and X-ray diffraction were employed to characterise silver nanocubes and nanorods. The growth mechanisms of silver nanocubes and nanorods were discussed by taking account of the formation of single crystal and multiply twinned seeds, respectively.