The first principles calculation within the full potential linearized augmented plane wave (FPLAPW) method is applied to study the structural, electronic and optical properties of cubical perovskiteXCaF3on the base of density functional theory (DFT).The exchange correlation effects are included through the generalized gradient approximation (GGA) exchange potential. The calculated structural properties such as equilibrium lattice constant, the bulk modulus and its pressure derivative are in agreement with the published results of other authors. From our study we have found that the band gap of KCaF3 and RbCaF3 are 6.1 eV and 6.3 eV respectively that indicates insulating nature of XCaF3 compound. Calculation of optical spectra such as real and imaginary parts of dielectric function, refractive index and absorption coefficient are performed on the range of energy 0 - 40 eV
