More: When to visit Thailand · Thailand travel guide
Quick Answer
The best islands in Thailand split between the Andaman coast — Phuket, Koh Phi Phi, Railay, Koh Lanta and the Similans, best from November to April — and the Gulf, where Koh Samui, Koh Tao and Koh Phangan stay good later into the year. Here are 10 of the best, with who each suits and when to go.
Thailand has more than a thousand islands, and choosing between them mostly comes down to coast and season. These 10 cover the full range — diving, climbing, partying, families and total escape — with what defines each and the best months to visit.
10 of the Best Islands in Thailand
1. Phuket
Thailand’s largest island is also its most complete: long west-coast beaches, an atmospheric old town, the Promthep Cape sunset and an international airport that makes it the easiest arrival point.
2. Koh Phi Phi
Sheer limestone cliffs enclose impossibly green water. Maya Bay is the headline, but the island’s real pleasure is longtail-boat days between hidden coves and snorkelling stops.
3. Koh Samui
The Gulf’s most developed island balances resorts and spas with quiet coconut-fringed bays, waterfalls and a genuine town at Nathon. Its season runs later than the Andaman coast.
4. Railay & Krabi
Technically a peninsula but reachable only by boat, Railay is ringed by karst walls that draw climbers from around the world, with white sand and lagoons between them.
5. Koh Tao
The cheapest place on earth to learn to dive, and deservedly popular for it — clear, shallow reefs, calm bays and a laid-back backpacker heart.
6. Koh Lanta
Long, quiet west-facing beaches and a slow pace make Lanta the Andaman’s family and long-stay favourite, with sunsets over the sea every evening.
7. The Similan Islands
A protected marine park of granite boulders and coral gardens, open November to May, and consistently rated among the world’s best dive and snorkel sites.
8. Koh Phangan
Famous for the Full Moon Party at Haad Rin, but most of the island is the opposite: jungle interior, empty northern bays like Bottle Beach and a growing wellness scene.
9. Koh Chang
Thailand’s third-largest island sits close to the Cambodian border, with a mountainous rainforest interior, waterfalls and quiet beaches along the west coast.
10. Koh Lipe
Tiny and remote in the far south, ringed by three beaches and sitting inside Tarutao National Marine Park — the clearest water in the Thai Gulf and Andaman.
Andaman or Gulf? How to choose
The two coasts run opposite seasons. The Andaman side — Phuket, Phi Phi, Krabi, Lanta and the Similans — is at its best from November to April, when seas are calm and visibility peaks. The Gulf islands — Samui, Tao and Phangan — shrug off that monsoon and stay good from roughly February to September, with October and November the wettest. Ferries link most islands cheaply; the Similans close entirely from mid-May to October to let the reefs recover.
Frequently Asked Questions
Which is the best island in Thailand?
Phuket for convenience and variety, Koh Phi Phi for scenery, Koh Tao for diving, and Koh Lanta or Koh Lipe for a quieter stay.
When is the best time to visit Thai islands?
November to April for the Andaman coast; February to September for the Gulf islands. Avoid the Gulf in October and November.
Which Thai island is best for families?
Koh Lanta and Koh Samui — calm, shallow beaches, short transfers and plenty of family-friendly places to stay.