Short answer
Mu Ko Similan National Park is open from 15 October to 15 May: the 2026–2027 season began on 15 October 2026 and runs to 15 May 2027. The rest of the year the park is closed for the south-west monsoon. Visitors are limited by a daily quota of 3,850 people, 525 of them for scuba diving, nobody may stay overnight on the islands, and day trips leave from Thap Lamu pier near Khao Lak, about 90 minutes from the islands by speedboat.
The Similans are open from mid-October to mid-May
Anyone who looks up the Similan Islands soon finds that they are not open all year. Mu Ko Similan National Park opens on 15 October and closes after 15 May. Thailand's Department of National Parks confirmed the official opening of the 2026–2027 season on 15 October 2026, and Pattaya Mail, reporting on the opening, gave the end of the season as 15 May 2027.
Between those dates the park is closed for the south-west monsoon, when the open sea between Khao Lak and the islands becomes rough and the reefs get a rest. Wikipedia gives the closed period as 16 May to 15 October. If your trip falls in that window, the Similans are not an option, and the sheltered bays closer to Phuket, such as Phang Nga Bay, are.
What the Similans are: eleven granite islands 70 km out
The Similans are not one island but an archipelago. Wikipedia describes the national park, established in 1982, as eleven islands about 70 kilometres off the coast of Phang Nga Province in the Andaman Sea. The islands have numbers as well as names: the park headquarters is on Ko Miang (Island 4), and the largest island is Ko Similan (Island 8).
Ko Similan is the one on the postcards. Above its main beach, Donald Duck Bay, stands Sail Rock, a granite boulder on top of the ridge that the Department of National Parks names as the park's highlight, together with its dive sites. The granite is what sets the Similans apart from the limestone towers of Phi Phi and Phang Nga Bay: white sand, rounded boulders and very clear water.
The daily quota and why the opening day is busy
The park limits the number of people who may visit each day. When it reopened in October 2021, the Department of National Parks set the limit at 3,850 visitors a day, split between day trips and scuba diving, with 525 places a day for divers. Wikipedia notes that the same limit was introduced when the park reopened in 2018, after an earlier average of about 7,000 visitors a day.
In practice the quota is felt most at the start of the season. On the opening day in 2026 the park counted 1,409 visitors: 1,359 on day trips and 50 divers. On a tour the operator registers every guest in advance, which is why the park asks for passport details: our Similan tour needs a passport copy for every guest by email no later than the day before.
No nights on the islands, and the islands you cannot land on
You cannot stay overnight on the Similans. Wikipedia records that all overnight accommodation on the islands has been removed; the only way to spend nights in the park is on a liveaboard dive boat, which sleeps on the water. For everyone else the Similans are a day trip, and the long ride in each direction is part of the price.
Some islands are off limits altogether. Wikipedia notes that Ko Tachai has been closed to tourists since October 2016, and that landing on Ko Huyong is prohibited because its beach is a turtle nesting site. The day-trip route keeps to the islands that are open: in our case Ko Bangu, Ko Similan, Ko Payu and Ko Miang.
How a day trip gets there: Thap Lamu pier and a 90-minute ride
Every day trip starts at Thap Lamu pier in Thai Mueang district, just south of Khao Lak. Pattaya Mail's report on the 2026 opening describes the routine there: tour operators check guests in, hand out equipment and give a safety briefing before boat trips of about 90 minutes. Life jackets are compulsory for every passenger during the crossing.
From Phuket the day is long. On our Similan Islands speedboat trip the minibus collects you between about 5:30 and 7:30 am, the speedboat leaves Thap Lamu at about 9:00, and you are back at the pier at about 4:30 pm, which means your Phuket hotel at about 6–7 pm. If you can spend the night before in Khao Lak, the pickup is much later.
What you see in a day: Donald Duck Bay, Sail Rock and the reefs
A day trip is built around snorkelling and one long beach stop. On our route the first stop is snorkelling from the boat at Ko Bangu (Island 9), then Donald Duck Bay on Ko Similan for a swim, lunch and the short, steep climb to the Sail Rock viewpoint. After lunch the boat stops at Ko Payu (Island 7), where sea turtles and clownfish are often seen, and ends at Ko Miang.
Wikipedia notes that the sea around the islands averages about 18 metres in depth, with coral reefs and granite rock formations; our operators rate the visibility around Ko Payu and Ko Bangu as the best on this coast. Nobody can promise turtles: they are wild animals. What you can count on is water clear enough to see the reef from the surface, which is the reason people make the long trip instead of a closer island.
The rules the park asks you to follow
Opening the 2026 season, the park chief listed what the rangers would be telling every visitor: use a sunscreen without chemicals that harm coral, cut out single-use plastics, and respect the conservation zones set up against illegal fishing. Thailand's marine parks have banned sunscreens with oxybenzone, octinoxate, 4-MBC and butylparaben since August 2021, with fines of up to 100,000 baht.
The other rules are those of any marine park: do not stand on or touch the coral, do not chase or touch turtles, and take everything you bring back to the boat. The national park fee is collected for every visitor; on our tour it is already included in the price, so there is nothing to pay on the day.
Which weeks are best inside the season
The whole season is not equal. From our operators' experience, December to April usually brings the calmest sea and the clearest water, while the first weeks after the October opening and the last before the May closing can be windier, and a trip is occasionally moved for weather. If the park or the operator decides the sea is unsafe, the trip is moved or refunded.
Our tour runs from 15 October to 14 May. If you are choosing between the Similans and a shorter day, the trade is simple: the Similans give the best water within reach of Phuket for a 12–13 hour day; Phi Phi is closer and more about famous beaches, with rules of its own at Maya Bay. Our Similan travel guide covers the rest of the day in detail.
Practical checklist
- Check that your dates fall between 15 October and 15 May; outside them the park is closed.
- Send a passport copy for every guest by email no later than the day before the trip.
- Plan for a 5:30–7:30 am pickup from Phuket, or stay the night before in Khao Lak.
- Pack a reef-safe sunscreen, swimwear, a towel and seasickness tablets if you need them.
- Wear sandals with grip for the climb to the Sail Rock viewpoint.
Questions and answers
When are the Similan Islands open in 2026 and 2027?
From 15 October 2026 to 15 May 2027. The national park closes every year for the south-west monsoon and reopens in mid-October.
Can you stay overnight on the Similan Islands?
No. All overnight accommodation on the islands has been removed. The only way to spend nights in the park is on a liveaboard dive boat.
How many people can visit the Similans each day?
The park's daily quota is 3,850 visitors, including 525 places for scuba diving. On the opening day of the 2026 season 1,409 people visited.
How long is the boat ride to the Similan Islands?
About 90 minutes by speedboat from Thap Lamu pier near Khao Lak, depending on the sea. From Phuket add the drive to the pier: pickup is between about 5:30 and 7:30 am.
Is the national park fee included in a Similan day trip?
On our Similan tour, yes: the national park fee is included in the price. Check this with any other operator before you book, because not every tour includes it.