Nanocrystalline spinel CuAl2O4 powders were prepared by sol-gel method from nitrate Cu(NO3)2·3H2O, Al(NO3)3·9H2O and complex C6H8O7·H2O. Sintering was carried out at 400, 500, 600, 700, 800°C respectively for 2 h in air. The XRD patterns started to appear CuAl2O4 peaks after sintering of 500°C and consist of only CuAl2O4 peaks as spinel crystal after sintering of 700°C. The powders were analyzed by TEM and UV-vis diffuse reflectance spectrum to be round, about 10–30 nm in size and Eg=1.77 eV. Photodegradation property of nanocrystalline CuAl2O4 powders was investigated by using methyl orange as model pollutant and mercury lamp (λ>400 nm) as energy source. The results indicated that CuAl2O4 powders sintered at 700°C had the excellent visible photocatalytic property. Under the irradiation of visible light, methyl orange could be degraded 97% in 120 min.