Unzen-Amakusa National Park has a mix of deciduous broadleaf forests and evergreen broadleaf forests. Japanese silver grass and Japanese red pine grow near steamy Unzen Jigoku, while the peat moss wetlands of Gensei Marsh are dotted with Japanese irises. Mount Unzen is covered with vibrant pink Kyushu azaleas in May, and flowering dogwood in June.
The park draws a variety of migratory birds that include the blue-and-white flycatcher, narcissus flycatcher and little cuckoo. Subtropical fish such as the sapphire devil and blacksaddle goatfish frequent the coral reefs off the coast.