St. Martin's Island (Bengali: সেন্ট মার্টিন্স দ্বীপ) is a small island (area only 8 km2) in the northeastern part of the Bay of Bengal, about 9 km south of the tip of the Cox's Bazar-Teknaf peninsula, and forming the southernmost part of Bangladesh. There is a small adjoining island that is separated at high tide, called Chera Dwip. It is about 8 kilometres (5 miles) west of the northwest coast of Myanmar, at the mouth of the Naf River.
The first settlement started 250 years ago by Arabian sailors who named the island 'Jazeera'. During British occupation the island was named St. Martin Island. During the First Anglo-Burmese War between the British and Burmese empires in 1824–1826, rival claims to the island were a major factor. The local names of the island are "Narikel jinjira"[3] which means 'Coconut Island' in Bengali, and "Daruchini Dwip" which means "Cinnamon island" in Bengali. It is the only coral island in Bangladesh.It is also the southernmost part among Extreme Points of Bangladesh.
It is possible to walk around the island in a day because it measures only 8 km2 (3 sq. mile), shrinking to about 5 km2 (2 sq. mi) during high tide. The island exists only because of its coral base, so removal of that coral risks erosion of the beach. Because of this, St. Martin's has lost roughly 25% of its coral reef in the past seven years.