The spectral dependence of Δn = no - ne of CdGa2S4 crystals in short- and long- wavelength part of isotropic wavelength λ0 = 485.7 nm (300 К) was determined. It was established what in the case when λ > λ0 Δn is positive and at λ < λ0 it is negative. The wavelength λ0 = 485.7 nm shifts in short - wavelength at decreasing of temperature. Ground and excited states of three excitonic series (A, B and C) with binding energies of 53 meV, 52 meV and 46 meV, respectively were found out at 10 K. The effective mass of electrons for k = 0 was determined form calculation of excitonic spectra (mc || (Е||с) = 0.21m0 and mc  (Ес) = 0.19m0). The holes masses are equal to 0.59m0, 0.71m0 and 0.71m0, respectively. The value of valence bands V1 - V2 splitting by crystalline field is corresponding to 24 meV and bands V2 - V3 splitting due to the spin-orbital interaction is equal to 130 meV.