Monodispersed TiO 2 spherical colloids with diameters of about 250nm were prepared by a sol–gel method. Heterostructural Ag–TiO 2 spheres were manipulated by surface engineering, in which the Ag nanoparticles with an average size of 10nm were uniformly distributed on the surface of the TiO 2 nanospheres by in situ reduction and growth. The gas-sensing properties of the TiO 2 nanospheres and heterostructural Ag–TiO 2 nanospheres to ethanol and acetone were measured at 350°C. The results indicated that Ag nanoparticles greatly enhanced the response, stability and response characteristic of TiO 2 nanospheres to the tested gases. Response times of Ag–TiO 2 sensor to 30ppm acetone and 50ppm ethanol were <5s.