Scanning electrochemical microscopy (SECM) was employed to quantitatively characterize the oxygen permeation behaviors of poly(dimethylsiloxane) (PDMS) and surface-modified PDMS. The mass-transfer process of oxygen from the PDMS substrate to the tip electrode is diffusion limited, whereas the oxygen permeability of PDMS subjected to oxygen plasma treatment or albumin adsorption is critically restricted. Our results suggest that the oxygen permeability of PDMS is possibly affected by O-2 plasma irradiation and albumin adsorption at the PDMS surfaces.