The linear viscoelastic behaviour of molecularly thin OMCTS (octamethylcyclotetrasiloxane) films has been studied as a function of film thickness using a modified surface forces apparatus. The frequency spectra of viscoelastic relaxation measured at different film thicknesses superposed onto a master curve when each spectrum was shifted horizontally and vertically with respect to the frequency spectrum at a reference film thickness. The master curve indicates a wide separation between two sets of viscoelastic relaxations and suggests a gradual glass-like transition to solidity.