The Tatamidō (Japanese: 畳胴; "Tatami Armor") is a Japanese armor of the Sengoku period. It belongs to the larger group of Tōseigusoku.
Unlike the typical armors of this time, the breastplate is not made of studded leather strips (Itazane), but of chainmail. This is not a Japanese invention, but a replication of European armors that reached Japan with the so-called Nanban trade.
The armor also included a foldable chainmail hood. The unusual name comes from the fact that the surface of chainmail reminds of Tatami mats. A Tatamidō armor is exhibited in the Central Museum of Chiba Prefecture (千葉県中央博物館).