The structure of thin films of molybdenum sulphide (MoS2) deposited on silicon substrates has been investigated as a function of temperature using X-rav diffraction and transmission electron microscopy. The initial state of the films is characterised by microcrystals with a diameter of around 2 nanometres. Thermal treatment leads to an increase in grain size to around 20 nm at 900-degrees-C. A continuous reduction in the c lattice parameter is observed during heating. Prior to heat treatment the structure of the film is dependent upon film thickness. Upon heating these differences are observed to disappear. Isothermal measurements of the diffraction pattern at elevated temperatures show only slight changes in the structure with time. The final state of the MoS2 is similar to that of bulk polcrystalline molybdenum sulphide.