The freezing resistance of winter twigs of genera which became extinct in Japan during Tertiary time, such as Sequoia, Metasequoia, Taxodium, Glyptostrobus, Pseudolarix, Keteleeria and Liquidambar, has been investigated. Except for Taiwania, Sequoia, Cunninghamia lanceolata, most of the genera were found to survive freezing down to – 20° to – 25°C, and Metasequoia and Taxodium to resist freezing down to – 25° to – 30°C. Most of the typical temperate deciduous genera native to Japan, such as Carpinus, Zerkova, Castanea, Acer and Cercidiphyllum, which lived together with the extinct genera during the Tertiary as common members of the Arcto-Tertiary Forest, were also found to survive freezing down to –20° to – 25°C. From the standpoint of freezing resistance, it therefore seems likely that most of the Arcto-Tertiary genera which became extinct in Japan could winter in the deciduous forests in Japan during late Tertiary time, unlike evergreen broad-leafed trees and some conifers such as Taiwania, Sequoia and Cunninghamia lanceolata. To clarify the reason of their distinction from the standpoint of cold injury, a further study on their resistance to winter desiccation is required.