Abstract The utilization of inorganic cubic perovskite semiconductors has increased their prominence within industrial applications pertaining to optoelectronic and photovoltaic devices. Lead-free materials are currently receiving significant attention among many perovskite compounds, mostly due to their environmentally non-toxic nature. In the present work, the structural, optical, electronic, thermodynamic and mechanical properties of inorganic perovskites FrBO3 (B = Ta, Nb) are discussed via generalized gradient approximation based on density functional theory. The band structure, density of states, absorption, dielectric function and reflectivity are calculated to describe electronic and optical properties of the compounds. The ground states lattice parameters are found to be 4.292 Å and 4.194 Å with direct band gap of 1.175 eV and 0.90 eV, respectively. The elastic constants and Debye temperature of FrBO3 showed that the compounds are mechanically and thermodynamically stable. The results obtained by this study reveal that FrTaO3 has superior absorption and conductivity making it a more suitable candidate for various optoelectronic devices.