Koh Khai Nui is part of the Khai Island group, located in Phru Nai Subdistrict, Ko Yao District, Phang Nga Province. Although administratively under Phang Nga, its close proximity—approximately 10 kilometers from Phuket—has made it a popular destination for day trips departing from Phuket’s piers. In terms of physical geography, Koh Khai Nui is distinctly different from nearby Koh Khai Nok and Koh Khai Nai. The island is essentially a small rocky outcrop covered with patches of green vegetation, with no sandy beach suitable for landing. As a result, all tourist activities are concentrated in the surrounding waters.

From an ecological perspective, Koh Khai Nui is recognized as one of the notable snorkeling sites within the Khai archipelago. The area around the island features shallow coral reef systems with considerable biodiversity, including Staghorn, Brain, and Table corals distributed along the submerged rocky terrain. Water clarity is typically high under favorable conditions, allowing good visibility of the marine environment. This ecosystem supports a variety of marine species, such as Sergeant Major fish, Clownfish inhabiting sea anemones, Giant Clams, and Sea Urchins commonly found along reef structures.

In addition to its underwater appeal, Koh Khai Nui also serves a minor geomorphological role as a natural buffer against waves during certain seasons, offering calmer conditions for small tour boats operating nearby. Visitors can admire the island’s distinctive rock formations, shaped over time by marine erosion, which have become recognizable photographic landmarks. Since there is no convenient landing area, human impact on the island itself remains relatively limited. This restricted access helps maintain a quieter environment and contributes to the preservation of the surrounding marine ecosystem to some extent.

• The easiest way is by speedboat from various piers in Phuket (such as Asia Marina or Rassada Pier). The journey takes approximately 15–30 minutes and is usually part of a "3 Khai Islands" tour package.

• Strictly avoid touching or stepping on corals to prevent injuries and reef damage.

• Check the weather forecast in advance; strong winds can make snorkeling risky.

• Keep a bottle of fresh water with you to stay hydrated while out in the sun.

• Follow the guide’s instructions carefully, especially in areas with stronger currents.

Admission Fees:

• Thai & Foreign Nationals: No direct admission fee to enter the island area (as there is no beach for landing).

• Note: Snorkeling and transportation costs are included in tour packages, which typically range from 1,000 to 2,500 THB depending on the boat type and departure point.

Opening Hours:

• Open daily from 08:00 AM – 05:00 PM.