Kāi Mamoe, or Ngāti Mamoe, is an historic Māori iwi. Originally from the Heretaunga (Napier) area they moved to the South Island in the 1500s — which at that time was occupied by the Waitaha.
Ngāti Mamoe were largely absorbed via marriage and conquest by the Ngāi Tahu who migrated south a century later. While today there is no distinct Ngati Mamoe organisation, many Ngai Tahu have Ngati Mamoe links in their whakapapa and, especially in the far south of the island, "...southern Maori still think of themselves as Ngai Tahu-Ngati Mamoe, a synthesis of the two tribal groups..."