In this mini-review, theoretical studies of some optical properties of cadmium sulfide nanocrystals in the ultraviolet spectrum are considered. A variational method was described by which the energy of the ground state of the electron-hole pair was obtained as a function of the radius of the cadmium sulfide nanocrystal within the effective mass approximation. A mechanism is proposed that describes the absorption of the considered nanosystem in the ultraviolet spectral ranges. It is shown that the absorption peaks of the nanosystem are caused by interband electron transitions from the energy quantum-confined level lying in the valence band of the CdS NC to the energy quantum-confined level located in the conduction band of the cadmium sulfide NC. It has been established that the formation of the energy quantum-confined levels of an electron and a hole in a CdS nanocrystal, is significantly affected by the energy of the Coulomb electron-hole interaction, as well as the energy of the polarization interactions of the electron and hole with the interface (nanocrystal – matrix).