Ba0.65Sr0.35TiO3 (BST) thin films have been deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and field emission scanning electron microscopy, respectively. The crystallization behaviour of the films is clearly affected by the substrate temperature, annealing temperature, and sputtering pressure. The thin films that are deposited at room temperature are amorphous in their as-deposited state. However, an improved crystallization can be observed for BST thin films deposited at higher temperatures. As the annealing temperature is increased, the dominant X-ray diffraction peaks become sharper and more intense. The dominant diffraction peaks increase with sputtering pressure, steadily increasing for films deposited from 0.37 to 1.2 Pa. When the sputtering pressure is increased up to 3.9 Pa, the films have a (110) + (200) preferred orientation. Possible correlations between the crystallization and the changes in the sputtering pressure are discussed. SEM measurements indicate that the films, which consist of small grains, are smooth and that the interface between the film and the substrate is sharp and clear.