We report on the intersection of spectral dependences of refractive indices n o and n e at the wavelengths 546nm (λ 0 ) and 450nm (λ 01 ) in CdGa 2 Se 4 single crystals. The value of difference Δn=n e −n o is equal to zero at the wavelengths involved. When placed between two crossed polarizers, the crystals of CdGa 2 Se 4 exhibit a transmission band at the wavelength of λ 0 =546nm (300K). The ground and excited states of three excitonic series (A, B and C) were found out at 13K in CdGa 2 Se 4 crystals, and other parameters of excitons and bands were determined. In the Г point of Brillouin zone the effective mass of electrons m c is equal to 0.14m 0 , and the effective masses of holes m v2 and m v3 are equal to 0.76m 0 and 0.94m 0 , respectively. The hole mass m v1 depends upon the direction of wave vector k: at polarization E∥c, k∥a the mass m v1 =1.15m 0 , and at polarization E∥c, k∥b m v1 =0.84m 0 . The values of valence bands splitting in the center of Brillouin zone by the crystal field (Δ cf =49meV) and spin–orbital interaction (Δ so =351meV) were determined. The optical functions n, k, ε 1 and ε 2 in polarizations E⊥c and E∥c for the energy diapason from 3 to 6eV were calculated from the reflectivity spectra by Kramers–Kronig analysis. The evidenced features are discussed on the basis of recent theoretical calculations of the band structure of CdGa 2 Se 4 crystals.