Are the Similan Islands Open?

Yes. The Department of National Parks (DNP) opens Mu Ko Similan National Park every year from 15 October to 15 May, and the 2026-27 season runs from 15 October 2026 to 15 May 2027. Every year from 16 May to 14 October the park is closed and no day trip runs. Dates through the season can be booked on Siam Adventure World’s Similan Islands Early-Bird Tour From Phuket and Khao Lak!, from US$121 a person (checked November 2026) with the park fee included.

The calendar above is the early-bird day, with 4,453 reviews (checked November 2026). It shows only dates the trip runs.

The short answer

Between 15 October 2026 and 15 May 2027 the islands are open for day trips, and every day trip on this site runs in that window. Outside it, the honest answer is not to plan a Similan day at all: the park is closed, and no operator can take you. Inside it, keep a spare day in your stay, because a day trip can be cancelled or changed when the sea is rough, and the park itself can close for a day or two in a storm.

The dates, from the park authority

DNP sets the season: open from 15 October to 15 May, closed from 16 May to 14 October, every year. The 2026-27 season opened on 15 October 2026, and on that first day the park counted 1,409 visitors, 1,359 of them on day trips and 50 of them divers (DNP, 16 October 2026). Older pages around the web still give other opening dates; DNP’s own notices for 2026 give 15 October, and the day trips that print a season agree, with 15 October to 15 May on Sawanu Travel Company Limited's speed catamaran, Delight Tours and Travels' day and Phuket Premium Charter's small-group catamaran.

When not to go

Every year from 16 May to 14 October the park is closed, so a trip to Thailand in those months cannot include the Similan Islands, whatever an older blog post suggests. In the open season, weather can still stop a day: on 19 and 20 October 2022 DNP closed the park by notice for a storm, and the trips build the weather in too. The early-bird day’s itinerary may change with the tide and the weather. Love Andaman's day trip can change its programme for weather or sea conditions. On Phuket Premium Charter's speedboat day, a trip cancelled or moved for weather or safety can be refunded in full or rebooked. If your dates are fixed and your stay is short, book early in the stay so a cancelled day can move.

The rules that come with the season

Since 4 October 2018 the park has been open for day trips and diving only: nobody stays overnight on the islands (DNP). Since 15 October 2025 every visitor needs an e-ticket, and foreign visitors are registered with their passport number; on a trip with the fee included, the operator buys the ticket for you, which is why some trips need your full name, passport number and date of birth at booking. Ko Tachai, north of the main group, is closed to visitors, and DNP has announced no reopening date (as of November 2026).

Check dates in the 2026-27 season

Book a date while the park is open

Prices, ratings and review counts from the GetYourGuide listings (checked November 2026). Operators price by date and season, so treat the figures as the shape of the market, not a quote.

Pairing it with Phi Phi

If you are weighing the Similans against a Phi Phi day from Phuket, or planning both, Phi Phi keeps its own calendar and sea conditions: phiphiislandtourfromphuket.com covers the Phi Phi months from Phuket in detail.