Nanocrystalline Bi12TiO20 powders were successfully synthesized using an electrochemical method, where Bi and Ti plates were used as the anode and the cathode. Their crystallization and dispersion strongly rely on the H3PO4 amount in the electrolytic solution. Only large-sized Bi12TiO20 microspheres can be obtained without H3PO4, while adding H3PO4 in an electrolytic solution will destroy the dense microspheres and weaken the adhesion among primary particles, forming well-dispersed nanocrystalline Bi12TiO20. XRD and HRTEM evidenced the coexistence of body-centered cubic phase Bi12TiO20 with the face-centered cubic phase in nanocrystalline samples, and ultra-violet-Vis absorption and photodegradation data verified their good response to visible light and excellent photocatalytic ability.