Kōjima (幸島) is a small island in the Sea of Hyūga off the shore of the city of Kushima in Miyazaki Prefecture, Japan.

Kōjima is best known as housing a field study site of the Japanese Primate Research Institute, where Japanese macaques are held in wild conditions for primatological study.

The buildings of the field station are on the mainland so as to minimise disturbance of the monkeys' behaviour.

Many investigations have been carried out, including studies of the changes that occur in social dominance over time.

Kōjima is the site of one of the best-known studies in animal culture, in which it was reported that one monkey acquired various skills such as washing sweet potatoes in water,[1] and that these skills then spread through the monkey troops by imitation.