Tokunoshima is the second largest island in the Amami islands, after Amami Ōshima, and the 15th largest island in Japan.
It is more generally included within the Satsunan and Ryukyu archipelagos.
Isolated from the other Amami islands, Tokunoshima is located halfway between Amami Ōshima and Okinoerabujima.

The island is of volcanic origin with a length of approximately 25 kilometers (16 mi) and width of 18 kilometers (11 mi).
Most of the administrative towns of Tokunoshima and Amagi are covered in mountains and rolling hills, with Mount Inokawadake at 645 meters (2,116 ft) above sea level as the island's highest peak.
Mount Amagidake in the north has a height of 533 meters (1,749 ft).
The administrative town of Isen along the southwestern slope of the island is more flat, with fertile soil suitable for agriculture.
The coast of the island is largely rugged and rocky with small sandy beaches scattered throughout as well as a series of large cliffs on the southwest edge of the island.
The island is surrounded by a coral reef.

A series of large offshore rocks known as Tonbura Rocks are a prominent feature in the ocean off the northeastern coast of the island.
The neighboring islands of Amami Ōshima, Kakeromajima, Yoroshima, Ukejima to the northeast and Okinoerabujima to the southwest are all visible from the island.
On exceptionally clear days, the twin volcanoes of Iōtorishima, in Okinawa Prefecture, can be seen to the west.

The island falls within a 
subtropical moist broadleaf forest ecoregion.
Although Tokunoshima is subtropical, it receives sufficient rainfall that it has rainforests.
Much of the island remains covered in laurel forests, although many areas have been extensively cleared for agriculture.
There are many caves on the island, the longest of which measures 2,052 meters (6,732 ft) and is located in the area of Isen.

The climate of Tokunoshima is classified as a humid subtropical climate (Köppen climate classification Cfa) with very warm summers and mild winters.
The rainy season lasts from May through September.
The island is subject to frequent typhoons.
Tokunoshima is the second largest island in the Amami islands, after Amami Ōshima, and the 15th largest island in Japan. It is more generally included within the Satsunan and Ryukyu archipelagos. Isolated from the other Amami islands, Tokunoshima is located halfway between Amami Ōshima and Okinoerabujima.
The island is of volcanic origin with a length of approximately 25 kilometers (16 mi) and width of 18 kilometers (11 mi). Most of the administrative towns of Tokunoshima and Amagi are covered in mountains and rolling hills, with Mount Inokawadake at 645 meters (2,116 ft) above sea level as the island's highest peak. Mount Amagidake in the north has a height of 533 meters (1,749 ft). The administrative town of Isen along the southwestern slope of the island is more flat, with fertile soil suitable for agriculture. The coast of the island is largely rugged and rocky with small sandy beaches scattered throughout as well as a series of large cliffs on the southwest edge of the island. The island is surrounded by a coral reef.
A series of large offshore rocks known as Tonbura Rocks are a prominent feature in the ocean off the northeastern coast of the island. The neighboring islands of Amami Ōshima, Kakeromajima, Yoroshima, Ukejima to the northeast and Okinoerabujima to the southwest are all visible from the island. On exceptionally clear days, the twin volcanoes of Iōtorishima, in Okinawa Prefecture, can be seen to the west.
The island falls within a 
subtropical moist broadleaf forest ecoregion. Although Tokunoshima is subtropical, it receives sufficient rainfall that it has rainforests. Much of the island remains covered in laurel forests, although many areas have been extensively cleared for agriculture. There are many caves on the island, the longest of which measures 2,052 meters (6,732 ft) and is located in the area of Isen.
The climate of Tokunoshima is classified as a humid subtropical climate (Köppen climate classification Cfa) with very warm summers and mild winters. The rainy season lasts from May through September. The island is subject to frequent typhoons.
Tokunoshima