BiOI/SiO2 catalysts with different loadings were prepared by precipitation?鄄impregnation method，and their performance of photocatalytic degradation of methyl orange was investigated.The catalyst was characterized by XRD，UV-Vis and TEM.The results showed that the photocatalytic degradation rate of methyl orange by BiOI/SiO2 catalyst increased with the increase of BiOI loading.When the amount?鄄of?鄄substance ratio of BiOI to SiO2 was 0.5，the degradation rate of methyl orange by BiOI/SiO2 catalyst could reach 73.74% in 60 min.The degradation rate of methyl orange of BiOI supported on SiO2 with different particle sizes was almost similar，because the active component BiOI could be highly dispersed on SiO2 supports with different particle size.