A neutral transparent SiO2/TiO2 composite hydrosol was prepared by a coprecipitation-peptisation method using titanium tetrachloride and SiO2 hydrosol as raw materials. The prepared SiO2/TiO2 hydrosols were characterised by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The evaluation of photocatalytic activity for nitric oxide degradation showed the optimal weight ratio of SiO2/TiO2 is around 1.5. After heating at 700°C for 1h, the prepared SiO 2/TiO2 hydrosol exhibits much higher photocatalytic activity than the commercial TiO2 materials, Degussa P25 and ONID TH. The presence of Ti-O-Si bond in the composite hydrosol results in its good thermal stability. The prepared transparent SiO2/TiO2 hydrosols were stable without agglomeration or gelation after storage at room temperature for over 1.5 years. The neutral SiO2/TiO2 hydrosol could be used as the coating material applying for glass or ceramic building materials which must be treated at high temperature.