Amanatsu(甘夏?) is a yellowish orange citrus fruit, a group of cultivars of natsumikan(ナツミカン（夏蜜柑）?, Citrus natsudaidai), which were discovered in 1740 in the Yamaguchi prefecture of Japan. Natsumikan is about the size of grapefruit and oblate in shape. The fruit contains 12 segments and about 30 seeds. In Japan, it is officially known as the kawano natsu daidai(カワノナツダイダイ（川野夏橙）?), but also colloquially the amanatsu, amanatsu daidai(甘夏橙), amanatsukan(甘夏柑), and amanatsu mikan(甘夏蜜柑（甘夏みかん）).
Natsumikan is grown commercially in Japan, notably in Kumamoto and Ehimeprefecture. The city of Hagi is famous for its natsumikans, particularly when used in natsumikan juice and ice cream. The rough textured fruit is easy to peel and is commonly eaten fresh. It is also used for wide variety of products ranging from marmalades to alcoholic beverages.
The natsumikan tree is believed to be derived from pomelo, Citrus grandis or Citrus maxima.