© 2020 Elsevier Ltd Bismuth molybdate low-temperature γ-phase (γ-Bi2MoO6) has been widely studied as catalytic compound, and a recent experimental study demonstrated that Ruthenium (Ru) doping on γ-Bi2MoO6 enhanced their CO to CO2 conversion capacity at low temperature. To elucidate the effect of Ru-doping on γ-Bi2MoO6 electronic properties, in the present work are calculated the electronic structure and optical properties of γ-Bi2MoO6 and Ru-doped γ-Bi2MoO6 (γ-Bi2MoO6:Ru) compounds, in terms of the Density Functional Theory (DFT), using the modified Becke-Johnson (mBJ) approximation to the exchange-correlation potential. The electronic band structure, the total and projected density of states (DOS and PDOS, respectively), the real and imaginary part of dielectric function, ε, and the absorption spectra of both γ-Bi2MoO6 and γ-Bi2MoO6:Ru compounds, were obtained after the structural optimization of its crystalline lattices. The results show that Ru doping contributes to the generation of electronic states into the forbidden region of γ-Bi2MoO6, leading to a band-gap reduction, increasing their absorption along the visible-light regime. Our results provide insights for the development of novel ruthenium doped bismuth semiconductors for catalytic-related applications.