Tin oxide thin films have been deposited on oxidised silicon substrates using a reactive r.f. magnetron sputter process with a tin target in a mixed oxygen/argon gas environment. Process parameters such as oxygen composition, substrate temperature and r.f. power have been varied and the resulting films characterised structurally using X-ray diffraction, atomic force microscopy and transmission electron microscopy (TEM). TEM has demonstrated that the films are composed of an amorphous matrix as well as columnar grains of SnO2 which are interspersed with pores. The deposition method is shown to be a useful way of fabricating nanocrystalline particles of tin oxide within an amorphous matrix and the results are briefly discussed in relation to their significance for the fabrication of tin oxide quantum dots and nanoclusters.