We propose a novel method for generating thin film coating for use on a platinum (Pt) electrode. This is accomplished by a plasma-polymerized film (PPF), which is deposited directly onto the substrate under dry condition. The resulting films are extremely thin (<100 nm), have good adherence to the substrate (electrode), and have a highly-cross-linked network structure. The PPF-deposited Pt electrode shows a high selectivity towards targeted species without decreasing the sensitivity (i.e. maintaining a high electrical signal). This property is partly attributed to size discrimination from a highly-cross-linked network structure in the film. Moreover, an acetonitrile PPF-deposited PI electrode showed accumulation ability for hydrogen peroxide detection; the sensitivity of the PPF-deposited electrode (30-59 nm of film thickness) is one and half times larger than that of bale electrode. Chronocoulometric data support this effect. A hexadiene PPF-deposited Pt electrode also showed high selectivity between dopamine and ascorbic acid compared with a hare Pt electrode; the selectivity ratio for PPF-deposited electrode (37 nm of film thickness) is 12, whereas that of the bare electrode is 4.6. We demonstrate and discuss mass transport behavior of electrochemical species through plasma-polymerized thin film on platinum electrode.