It is shown that Raman spectra of nanocrystals with complex geometric shape can acquire additional broadening. In order to describe complex geometric shapes of nanocrystals in terms of its influence on the Raman spectrum, a parameter was introduced for the shape – roughness parameter. The roughness is defined as a relative parameter of the presence of additional volume on the faces of the cubic nanocrystal. The calculations for additional broadening of the Raman spectral line were made for 3–10 nm nanodiamonds.