In this paper, adsorbed polybutadiene (PB) layers onto solid substrates have been studied with two different molecular weights and different terminated groups. Spin cast PB film (originally around 25 nm in thickness) prepared on two kinds of preconditioning (with and without HF etch) in silicon substrates. The samples were annealed at 150??C for 10 h under vacuum and subsequently rinsed with toluene (a good solvent for PB) extensively. The residual PB layers were characterized by using X-ray reflectivity, and the result showed that the adsorbed layers were well fitted by a 3-layer (a silicon substrate, a native oxide, a polymer layer) model for non-end functionalized PB and a 4-layer model (a silicon substrate, a native oxide, a high density polymer layer and low density polymer layer) for hydroxyl PB adsorbed layer, respectively. Further experiments using supercritical carbon dioxide (scCO2) as a screen solvent proved that the interfacial energy is a key to explain the difference in the structures between the two polybutadiene adsorbed layers.