Reflection and wavelength modulated reflection spectra were investigated at temperature 10 K in CdAl2S4 crystals. Ground and excited states of three excitonic series (A, B and C) were found out. Contours of reflection excitonic spectra were calculated and main parameters of excitons and bands in k = 0 were determined. The effective mass of electrons mc is equal 0.30m0 and holes masses mv1, mv2 and mv3 are equal to 1.55m0, 0.90m0 and 2.07m0, respectively in Γ point of Brillouin zone. Valence bands V1 - V2 splitting due to crystal field (141 meV) and bands V2 - V3 splitting by spin-orbital interaction (152 meV) were estimated. Fig. 1 A - spectral dependencies of refractive indices (n|| and n) and its difference (Δn = n|| - n); B - spectra of permittivity imaginary parts (ε2|| and ε2) and theirs difference (Δε2 = ε2|| - ε2) for E||c and Ec polarizations and CdAl2S4 crystals. Three groups of maxima were discovered in reflection spectra in intrinsic region. The most long wavelength group was formed in the region of excitonic transitions (A, B and C). The second group of maxima is situated at energies 3.9 – 5.2 eV and the next high energy group at 5.2 – 6.5 eV. Spectral dependencies of refractive index (n), imaginary part of permittivity (ε2) and its differences (Δn and Δε2) were calculated by Kramers-Kronig method from measured reflection spectra, Fig. 1. Also spectral dependencies of extinction coefficients (k and k||), its difference (Δk = k- k||), phases (φ|| and φ) and a phases difference (Δφ = φ - φ||) were calculated for E||c and Ec polarizations at temperature 80 K. Features for all calculated optical functions have a good correlation with features observed in measured reflection spectra of CdAl2S4 crystals. Spectral dependencies of refractive indices n|| and n intersect in three energies: 4.474 eV, 4.924 eV and 5.303 eV (marked as λ0, λ1 and λ2). The difference Δn = n|| - n crosses the zero axis at the same energies (wavelength), Fig. 1, A. Spectral dependencies of imaginary parts of permittivity in E||c and Ec polarizations (ε2|| and ε2) and its difference (Δε2 = ε2|| - ε2) have the same features at the same wavelengths, Fig. 6, B. The intersection of spectral dependencies of refractive indices indicates that the crystal is isotropic and does not recognize the light polarization at these wavelengths. Such regularities show optical activity and take place in a lot of crystals including AIIB2IIIC4VI compounds.