The surface morphologies and compositions of the asymmetric films of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) prepared by in situ and ex situ oxidization with the KMnO4 aqueous solution and KMnO4/H2SO4 mixed solution were investigated by using scanning electron microscope, atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-FTIR). The effect of the oxidization reagents on morphological changes and the influence of in situ and ex situ preparation methods on surface compositions were discussed. Different from the in situ oxidation by degrading the copolymers to form a gradient film, the ex situ oxidation preferentially degraded the uppermost layer of the film. Although both the KMnO4 oxidation and the KMnO4/H2SO4 oxidation gave hierarchical structures, distinctive differences were found that large ridges and smaller granules were fabricated in the former film and the latter produced large and deep ravines and fine sponge-like morphologies. Additionally, the oxygen concentration and the oxo-species implanted by these oxidation treatments were characterized and evaluated to provide a quantitative comparison. Oxygen, as well as manganese was found to be implanted in the surface layer of the oxidized film, forming predominantly O-C and O-C=O groups, as well as a small fraction of O-H and Mn-O compounds. Changes in contact angle of water on these films and total surface oxygen content are related but not directly. The hystereses of water contact angle at a value of 119 +/- 3 degrees due primarily to surface roughness and at a value of 63 +/- 3 degrees due primarily to chemical heterogeneity are led by different oxidation degrees and oxidation methods. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2262-2273,2010