An efficient, quick and pretty accurate interference method for determining dispersions of ordinary no and extraordinary ne refractive indices and optical anisotropy of nematic liquid crystals, i.e., ne(), no() and n()ne()-no(), as functions of wavelength (in visible and near infrared region), is presented. The method relies on measurements of positions of interference fringes in spectrogram produced by a flat-parallel nematic liquid crystal cell in only one run.