The effect of pinhole-ratio and film conductivity on corrosion behavior of carbon steel covered with ceramic films formed by plasma CVD and ion plating (it was called inorganic-coating steels) was investigated in synthetic seawater. Pinhole-ratio of inorganic-coating steels was estimated on the basis of charge transfer resistance R_ct obtained in the impedance measurement in H₂SO₄ solution. Corrosion rate of inorganic-coating steels in synthetic seawater increased with increasing pinhole-ratio. This relationship on insulating film-coating steels was clearer than that on conductive film-coating steels. The results of polarization curve and scanning vibrating electrode measurement indicate that conductive films and carbon steel constitute galvanic couple in synthetic seawater. So corrosion rate of conductive film-coating steel is about ten times as large as that of insulating film-coating steel at the same pinhole-ratio. In conductive film-coating steels, maximum pit depth and pit number is characterized by film species after immersion test.