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In this study, structure, elastic, electronic and optical properties of cubic perovskite BiGaO3 and BiInO3 are calculated using the full-potential linearized augmented plane wave method in the density functional theory (DFT) using WIEN2k software. The calculated crystal structure of BiGaO3 and BiInO3 reveals that both compounds possess cubic crystal structure with pm-3m space group. The calculation of the structural parameters of both compounds confirms that the LDA gives a better value of the lattice parameters as compared to the GGA- WC and GGA-PBE. The calculated band gap for BiGaO3 and BiInO3 with GGA-mBJ reveal that these compounds exhibit semiconducting behavior with an indirect band gap between the occupied O 2p and unoccupied Bi 6p orbitals. From the density of states (DOS) calculation of both compounds, four regions due to the contribution Ga 3d orbital states, Bi/In 6s orbital and O 2p orbital states are clearly identified. It is also found that there exists a strong ionic bonding between Bi and O and a mixture of ionic and covalent bonding between Ga and O as well as In and O. The calculated elastic constants for BiGaO3 and BiInO3 with GGA-WC method indicates that both compounds are mechanically stable at ambient condition. To investigate the optical properties ofBiGaO3 and BiInO3compounds, the real and imaginary parts of the dielectric functions, refractive index, reflectivity spectra, extinction coefficient , optical absorption coefficient and electron energy loss function and real part of optical and optical conductivity are calculated with mBJ-GGA method in the photon energy range of 0 to 30 eV. A similar effect is observed in both BiInO3 and BiGaO3compounds.