Combined ab initio and experimental study of Mg-, Ca-, Sr-, Ba-doped bismuth titanate pyrochlores (BTO) has been carried out. It is revealed that the substitution of bismuth atoms by alkaline earth elements is a preferable process rather than the substitution of titanium atoms according to the structural and energy parameters from the first-principles calculations. The pyrochlore-type compounds Bi1.5Mg(Ca)(x)Ti2O7-delta have been obtained at x = 0.25. Bismuth titanate pyrochlores doped with Mg and Ca are wide-band semiconductor materials with the maximum of light absorption at wavelengths < 450 nm. The impedance study of new pyrochlore compound Bi1.5Ca0.25Ti O-2(7-delta) was carried out. Ca-doped BTO is a mixed electronic-ionic conductor with the activation energy of bulk conductivity about 1.00 eV in the temperature range 200-750 degrees C.