The nonstoichiometric Bi_3.64Mo_0.36O_6.55 photocatalysts were synthesized by a chemical bathing method and a wet ultrasonic-assisted chemical synthesis method respectively. The phase, morphology and optical property of asprepared products were investigated by X-ray diffraction(XRD), field emission scanning microscopy(FESEM) and optical absorption spectrum. The results showed that BMO-1 products obtained by sonochemistry reaction are single cubic crystal quasi-cubric nanoparticles with about 30~50 nm in diameter. The photocatalytic performance was evaluated by the degradation organic dye MB under the xenon lamp irradiation. Findings suggested that BMO-1 samples display the superior photocatalytic activity, of which the apparent reaction rate constant is 1.8 and 15.5 times that of BMO-2 and commercial nano TiO₂ (P25) respectively.