The preparation of strontium bismuth tantalate (SBT) thin films at low temperatures for electronic applications is at present the subject of intense study. However, the microstructural evolution of these films has not been extensively reported, despite its importance in the determination of the final properties of the film. In this work, we study SBT thin films with various nominal compositions obtained by the crystallization at 650degreesC of spin-coated solutions on a silicon-based substrate. Both the formation of the perovskite phase and the evolution of the grains are analyzed, with special attention to the formation of platelet-like grains. A process of coalescence of initially round grains is proposed to explain the grain growth in this system. We also show that the use of a preannealing step inhibits the grain growth and, therefore, should be avoided. The role that the film thickness plays in the development of large grains is discussed.