The results of doping influence on grain structure and their thermal stability of the SnO2 film are presented in the given report. The SnO2 films doped by Fe, Cu, Ni, Co (1-16 at.%) were deposited by spray pyrolysis from 0.2M SnCl4–water solution at Tpyr 350–450 oC. As it was reported earlier such transition metals existing in the form of metal oxides atomically dispersed or as clusters sufficiently affect on conductometric gas response of SnO2 thin film. The amount of doping concentration affects in nonlinear way both on film structure and electrical characteristics. The annealing at 850–1030 oC was carried out in the atmosphere of the air (~1 hour). The change of such parameters as film morphology, the grain size, texture and the intensity of X-ray diffraction (XRD) peaks have been controlled. For structural analysis of tested films we have been using X-ray diffraction, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) techniques. It was established, that doping by above mentioned transition metals during spray pyrolysis deposition does not improve thermal stability of the SnO2 film’s structure in studied range of annealing temperatures 600– 1000 oC. Moreover, such additives as cooper, stimulate noticeable grain’s growth during the process of high temperature annealing in comparison with the grain size change in undoped SnO2 films. It was concluded that observed effect was attributed to increased contents of the fine dispersed phase (<2-3 nm) arising in doped SnO2 films. The bigger contents of the fine dispersed phase are in as- deposited films, the greater is the change of the grain size after thermal treatment. At that the contents of this phase are being increased in the line SnO2, SnO2:Ni, SnO2:Fe, SnO2:Co, and SnO2:Cu. It was assumed that the fine dispersed phase, filling inter-crystalline space, besides a coalescence of the big grain creates conditions for mass transition from one grain to another one, necessary for coalescence of bigger crystallites, forming film. After annealing the morphology of doped and undoped SnO2 films becomes similar. The grains lose clearly defined faceting. Such unexpected influence of additives on the SnO2 films structure, i.e. the decrease of the grain size in asdeposited SnO2 films in comparison with undoped films and the increase of the grain size after annealing, forces researchers to be careful while elaborating the technologies of gas sensing layers’ deposition on the base of doped and multi-component materials. For example, the presence of the fine dispersed phase could be a reason of instability of the metal oxide films’ structure and generate temporal drift of the parameters of gas sensors, manufactured on their base. Therefore, while choosing additives for either the gas sensor optimization or for the film structure stabilization one should take into account that after changing of the conditions of synthesis, exploitation, or parameters of post-deposition thermal treatments, the consequences of the doping could be substantially different from the ones, observed during initial tests with as-deposited films.