To give more detail morphology and structure of the as-prepared composite, the TEM and high resolution transmission electron microscopy (HRTEM) characterizations were carried out. Fig. 3(a) and (b) shows the TEM images of the as-prepared SnO2-Pd-Pt- In2O3 composite. At first sight, the composite is composed of three morphologies. The SnO2 microspheres are superimposed together, up to hundreds of nanometers in diameter, and are composed of numerous primary nanocrystallites with average sizes of about 8 nm. The diameter of In2 O3 sheet is evaluated to be around 50–60 nm, which is consistent with the value estimated in XRD. The rest of the nanoparticles are Pd or Pt. Fig. 3(c) and (d) presents representative HRTEM micrographs of the as-prepared SnO2-Pd- Pt-In2O3 composite, which obviously display clear well-developed lattice fringes, implying a high crystallinity of the SnO2 -Pd-Pt-In2 O3 composite. The high crystallinity is able to facilitate the adsorption of gas molecules, so it is expected to contribute significantly to the enhancement of gas sensing performances [29].