Ko Sire (เกาะสิเหร่), also Ko Si Re, Ko Si Le, is an island off Phuket. The name is pronounced "Sih Reh" (two syllables).

Separated from the mainland of Phuket by the Khlong Tha Chin, a shallow mangrove swamp, this twenty-square kilometre island is connected by a causeway to the city.

• Wat Ko Si-Re, on the hill, has a large reclining Buddha and provides fine views of the surroundings.
• Phuket's largest settlement of sea gypsies (Chao Le), can be found on Ko Si-Re at Laem Tuk-Kae. The muddy seabed means the island is not good for swimming.

• . Visit the Sea Gypsy community. It may seem run down and dirty, but the people are real and have genuine smiles! 

There are some popular seafood restaurants on the eastern shore.