Most of the iron objects dug out from the archaeological sites in Japan have been corroded. The further corrosion of cast iron objects proceeds after excavation, and the objects become to decay quickly. For the conservation of the iron objects, which are common cultural properties from our ancient, for the coming age, it is of great importance to know the origin or process of corrosion. The distribution of the corrosion accelerating anions (such as chloride ion or sulfite ion.) have been investigated in these cast iron objects of 16th-19th century. The hyper-eutectic iron object contained chloride ion at center of carbon flakes in metallic and its surface have been corroded with a scale pattern at plates of carbon flakes. The iron objects with Ledeburite structure show strong corrosion resistant, but it cracks to a fine block and decay. An iron object of 19th century has been kept the shape with the eutectic of the phosphide compound, called steadite structure. The types of corrosion process of the archaeological cast iron objects have been controlled by the metallographic phases.