Amanatsu (Citrus x natsudaidai, also known as natsu mikan and daidai mikan) is a yellowish orange citrus fruit, about the size of grapefruit and oblate in shape. It is grown commercially almost exclusively in southern Japan, most notably in Kumamoto prefecture, where it is used for wide variety of products ranging from marmalades to wines.

The name Amanatsu (甘夏), which means "sweet summer" in Japanese, probably comes from the fact that the fruit is quite late in maturing. Amanatsu tree is believed to be a hybrid of pummelo (Citrus maxima) and mandarin orange (C. reticulata).