Molecular dynamics simulations were employed to investigate chain-length effects on conformations of methyl methacrylate (MMA)-oligomer thin films on an Au(111) substrate. Some observations were obtained from the present research. For short chain films, there is a sharp peak in the density profile of the MMA monomers for the adsorption region and the thin films exhibit a flattened conformation in the adsorption and the surface regions. For long chain films, however, there is no sharp peak in the whole density profile and a snake-like conformation appears in the adsorption region, which shrinks and convolutes gradually in the bulk region and even more in the surface region of the thin film.