The wide band gap of complex oxides is one of the major obstacles limiting their use in photovoltaic cells. To tune the band gap of complex oxides, this study examined the effects of chemical/oxygen vacancy doping on Bi4Ti3O12 based oxides synthesized using a solid reaction method. The structural, optical and electrical properties of the synthesized powers were determined by x-ray diffraction, scanning electron microscopy, ultraviolet-visible spectroscopy, and resistant measurements. Both types of doping, chemical doping and oxygen doping, could affect the tunability of the band gap. On the other hand, the decrease in band gap from oxygen vacancy doping was much more significant in the chemical doped sample than in the sample without chemical doping. Two stage doping, which combined chemical and oxygen vacancy doping, of La doped bismuth titanate reduced the band gap of La doped bismuth titanate from 2.75eV to 1.2eV without breaking symmetry.