Bismuth molybdate photocatalysts were controllably prepared via an electrochemical approach at room temperature. The composition and optical property of each product were determined according to the NaOH and Na2MoO4 quantities in the electrolyte. Pure Bi3.64Mo0.36O6.55 was prepared at a NaOH concentration range of 0.2-0.8molL(-1), whereas the Bi3.64Mo0.36O6.55/Bi14MoO24 composite was obtained in an electrolyte containing 0.4molL(-1) NaOH and 0.5molL(-1) Na2MoO4. The results of rhodamine B degradation under visible light indicated that Bi3.64Mo0.36O6.55 nanoparticles with a size of 10-50nm displayed the best photocatalytic efficiency, which was considerably higher than that of composite one and bulk Bi3.64Mo0.36O6.55.