The transformation behaviors of Sn²⁺-doped titania gels, such as transformation temperature, conversion rate and the crystal granularity, were studied by using thermo-gravimetric/differential thermal analysis and X-ray diffraction methods. Experimental results show that, anatase, rutile and SnO₂ phases can exist in the sintering products by varying Sn²⁺ content and sintering temperature. Sn²⁺-doping greatly depresses the growth of anatase and rutile crystals and so obtaining nanosized crystals The transformation temperatures of gel to anatase and anatase to rutile first decrease and then increase with an increase of Sn²⁺ content, while both of the transformation rates are associated with Sn²⁺ content, change in its valence and the sintering temperature. It is suggested that by adjusting Ti⁴⁺/Sn⁴⁺ ratio and sintering temperature, the crystal granularity and the ratio of anatase to rutile can be tailored to optimize properties of TiO₂–SnO₂ humidity sensing ceramics.