Zadetkyi Island or Zadetkyi Kyun (Saint Matthew's Island) is an island at the southern end of the Mergui Archipelago, Burma. Having a length of about 35 km and an area of 176 km², it is the largest island of the southern group. It has two prominent peaks, the highest of which is 864 m and is located near the middle of the island, at its southern end rises a 585 m. The island is hilly and densely wooded and lies 2.5 km south of Hastings Island.[1] Its northern side forms the southern shore of Hastings Harbor, where there is a base of the Myanmar Navy.
The Alladin Islands, the largest of which is Than Kyun, are a scattered cluster of islands extending to the W and SSW of Zadetkyi Island.