Liquid-liquid phase transfer has been used to synthesize platinum nanocrystals with a cubic morphology. By finely tuning the parameters controlling the nucleation and growth processes., nanometric truncated cubes or perfect Cubes may be obtained. To our knowledge(,e, this is the first time such shapes are obtained with this procedure. The importance of both the length of the capping agent to control the growth process and the bromide anions as poison for the {111} facet is shown. The low degree of size polydispersity allows these nanocrystals to self-assemble with a long-range ordering in two-dimensional and three-dimensional supracrystals. According to the nanocrystal shape, simple cubic or face-centered Cubic supracrystals are observed. It is remarkable to notice that well-faceted supracrystals with sizes oil the order of 10 mu m may be obtained.