In the Middle Pleistocene, some Manchurian or North Chinese Steppe horses are thought to have migrated into Japan.

Horses are poor swimmers so experts believe they arrived in Japan via a land bridge during a period of low sea levels during the Pleistocene (18k - 35k years ago). They are thought to have arrived from either Korea via Northeastern China or from Russia due to the fact that larger horses lived in both areas. Fossil records do support both theories, however. There have been fossil remains found in Japan that could support both.

Some experts believe that this population may have died out, however, since Chinese accounts tell of Kofun-era (250 - 538 AD) Japanese people being without horses. It could also have been that the horse population was so small that they were simply not visible to the visiting Chinese. Some accounts say that horses were not domesticated prior to this. They were hunted and eaten instead of being used as work animals.

From Kofun forwards, there is plenty of evidence showing that the Japanese domesticated horses