Spinel copper aluminate (CuAl 2 O 4 ) nanoparticles were synthesized with the aid of sonication by a precursor approach. The precursors were prepared by sonicating an aqueous solution of copper nitrate, aluminium nitrate, and urea. Upon heating at 900°C for 6h, the precursor formed nanosized CuAl 2 O 4 particles with an average size of 17nm and with a surface area of about 110m 2 g −1 . The nanosized copper aluminate particles as well as the precursors were characterized by elemental analysis, powder X-ray diffraction, transmission electron microscopy (TEM) image with electron diffraction pattern, thermogravimetric analysis, differential scanning calorimeter (DSC), Fourier transform of infrared spectroscopy (FT-IR), and Brunauer–Emmett–Teller (BET) surface area measurements. The photocatalytic degradation was investigated using methyl orange under the irradiation of Hg lamp (λ>400nm). The resulting degradation rates of the methyl orange were measured to be as high as 98% in 2h.