Noble metal (Au, Pd, Pt) loaded SnO2 sol solutions have been synthesized under hydrothermal condition. The mixed solution of noble metal chloride (HAuCl4, H2PtCl6, or PdCl2) and SnCl4 was neutralized with NH4HCO3 solution. The precipitate gel obtained was thoroughly washed and finally treated under hydrothermal condition (200 oC for 3 h at pH10.5) to obtain transparent sol solution. From SEM and TEM images of powder or thin film derived from sol, any noble metal particles could not be observed. However, the grain growth was suppressed when calcined at 900 oC for noble metal loaded SnO2. The peaks of Sn3d and O1s levels in XPS were shifted to the lower binding energy side. The electrical resistances of thin films prepared from noble metal loaded SnO2 sol were larger than that of pure SnO2 thin film. These results suggested that the noble metals were certainly loaded on SnO2 surface or included in the film to modify the surface state of SnO2.