The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi2O3–MoO3–B2O3. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (Eopt) and changes in cut-off (λc) depending on composition are reported. It was established that the increase in the MoO3 content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.