In this paper, a new method to synthesize ultrafine SnO2-TiO2 coupled particles is presented. The coupled particles are synthesized by homogeneous precipitation and characterized by EDS, XRD, TEM, HREM and BET surface area analysis. The coupled particles, pure ultrafine TiO2, commercial TiO2,and pure SnO2 are employed for photocatalytic degradation of azo dye active red X-3B in aerated solution. The results show that a very rapid and complete decolorization of the azo dye can be achieved, and the photoactivity of the coupled particles is higher than that of pure ultrafine TiO2 and commercial TiO2 particles, and the optimum loading of SnO2 on TiO2 is 18.4%. The enhanced degradation rate of X-3B using SnO2-TiO2 coupled photocatalysts is attributed to increased charge separation in these systems.